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Drag Racing Suspension and Setup for Type 1
by LhYnxz Thu Nov 27, 2008 3:52 pm
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| In this article we cover some basic car setup for VW Drag Racing. The information in this article, properly applied, may be able to keep you from breaking and/or crashing your car, or at the very least keep you from scaring the living daylights out of yourself (and/or your spouse, track personnel, or spectators at the track!) This article is NOT a safety article intended to keep you from getting hurt IF you crash -- For that we recommend you consult the NHRA rulebook. Many of the principles below apply to other cars, but since our specialty is rear engined VW, that is the focus of the article. Some of the issues I deal with in this article might seem like common sense, but after looking at many of the "race cars" out there, you stop assuming that common sense is common anymore! The faster your car is, the more critical your preparation for racing is, because you are putting more force and stress through the parts, AND because if something goes wrong, there's a lot less time to get out of trouble in a fast car then a slower one! So you can get away with the ghetto Engineering on a 15 second car or slower, but once you get faster and into the 11-12 sec range (or worse yet even faster), we are of the opinion that you shouldn't mess around. At those speeds we are talking about protecting both your car and your physical well being! I'm not going to get into safety devices (helmet, seat belts, roll cage, fire extinguisher, etc) in this article, I'll just say concisely that you need ALL of them. Let's continue...... During a Drag Race, there are two periods of severe suspension stress that need to be addressed: 1) the Launch 2) the Top End (which is slowing down safely after you've been going fast) If we only had to set the car up for ONE of these, the job would be much easier, since many times what works for one hurts the other! Setting up a car for Drag Racing is a series of compromises -- you'll see what we mean as you read this article. Steering Wheel Is it tight? Is it straight? I've seen many-a-car with loose steering wheels (loose screws? And I'm not talking about the steering wheel). A straight wheel might not seem very important, but once you've been crossed up at 110mph, you'll understand how nice it would be to have a wheel that's on straight for a frame of reference instead of having to operate on "feel". Many elite racers put a piece of tape on the top-center of their wheel so they know when it's straight if they have a problem; you are not as good a driver as they are (neither am I), so if it's OK for them, then you shouldn't be embarassed to do it in your car! If you are really hung up on it, you can take it back off after racing to preserve your pride. Another steering wheel issue is the distance of the wheel to the driver. Make absolutely sure that the steering wheel is not touched by the driver's knee during a run, which commonly happens during a gear change. It is absolutely critical that this doesn't happen, because in a fast car any unplanned bump to the wheel can initiate a wiggle to the car. Wiggles upset the lateral stability of a drag car with slicks to a degree you would find hard to believe. Tom Simon (a reputable VW Racer) has stood on the starting line and seen certain cars consistently get loose at the 1-2 shift, and witnessed the steering wheel wiggle. When I spoke with Tom recently, he made the following observation: "I watched the same car run-after-run do the same thing, and then it hit me: the driver's knee was hitting the steering wheel at EVERY SHIFT! Talk about dangerous. I asked the driver about it and he had no idea it was happening." So make sure this isn't an issue for you. Diligently replace worn out parts, and replace with top quality It may seem obvious, but do regular checks to ensure that your car has no loose or worn out parts. You ever wonder why airline mechanics are so anal and delay flights for the smallest hint of "mechanical difficulty"? It's because there is so much to lose if something goes wrong in the air! Well, at the high speeds you'll be going on the drag strip, you have a lot more to lose too! Parts to be extra careful to check and keep in good repair are: These must all be tight or at least minimal play! There is little point in aligning your car if the moment you move it off the alignment rack all the adjustments change because you have worn out stuff that allows your steering and suspension components to shift! It's also worth noting that you should not UNDER ANY CIRCUMSTANCES use screw in wheel studs. These are the cheesy, budget-threaded inserts that thread into your drums, then use a wheel nut. If you are using wheel nuts, then you must STUD the drums, with a press in stud from the backside. Yes press in studs are a pain, but it's a matter of safety. Screw-In Studs are just plain dangerous (and illegal on the track for a reason!). You are asking for something bad to happen if you use them. However, stock wheel bolts are fine, and perfectly safe. If you do stud the drums, make sure the studs are long. The Tech Inspectors like to see a bunch of threads beyond the wheel nut (like another 25mm/1"), that way even if the wheel nut comes loose, it won't immediately come off altogether. Narrowed Beams In my opinion, the only reason to use a narrowed beam is to fit the tires JUST inside the fenders. If you use an ultra narrowed beam for "the look", the car is not going to be as stable as it would be with a wider front track. Think about it -- a tricycle tips over much easier than a four- wheeled wagon. It's your call, but I think some guys are asking for it with their excessively narrowed front ends. Caster Caster is the "steering rake" angle that self-centers the steering. For actual alignment specs, you want enough caster to have the car go straight and be stable at speed. A good analogy can be observed with bicycles; slow speed bikes (mountain bikes) have more vertical forks (minimal caster), which makes their steering very responsive at slower speeds. But it also means you have to have a death grip on the handlebars when you are going fast, because the bike wants to turn all by itself if you don't. By contrast, a high end road bike will have a lot of caster, making it stable at high speeds, but more difficult to control for slow speed manoevring. Caster is the reason why you can easily ride with "no hands" on a road bike, but it's likely to put you in the hospital if you try the same on a mountain bike! Cars have the same characteristics. The stock VW did not have much caster off the showroom floor, for 2 main reasons: These 2 reasons are also what can make the VW a very harrowing experience to drive at speeds faster then designed (aka: racing). So the FIRST thing you should do right from the get-go is add some caster to the steering. On a standard beetle or ghia, you add Caster Shims between the lower tube of the front axle beam and the frame head (on the floor pan). On a Superbeetle you use Caster Fix Bushings which pulls the bottom of the strut forwards, accomplishing the same thing. Some Superbeetle owners also slot the upper strut mounts to move the top of the strut BACK. These methods all add rake to the steering angle, which stabilizes the car at higher speeds. The downside to additional caster is that it makes the car more difficult to turn at lower speeds, so only add just as much as you need to go nice and straight at your target speed. I suggest adding 1pr of shims if you're going from 70-90mph, and 2 sets of shims if you are going faster than that. The shims will really help give your car a more "solid feel". The increased caster will be especially noticeable and appreciated when you go through the finish line and let up off the gas and start braking, which both lowers the front and raises the back, seriously decreasing any caster the car already had! Front Camber Camber describes the straight up/down relationship of the tire. This one is easy -- Make them as straight up and down as you can. Guys that corner hard set the tops of the tires IN (bottoms out), so that the tire will be closer to vertical in a hard corner (when the car is all leaned over). Since we are drag racing and trying to go in a straight line, you want to make the camber as close to 0 as possible. Front Toe For a drag car, you want a TOUCH of toe-in up front; this reduces "scrubbing" (sideways movement of treads against the road). Excessive "scrub" can hurt your MPH going thru the traps. Toe out is twitchy and simply dangerous! 1/16-1/8" Toe-In is a good number to shoot for. When you check and set toe, do it on the ground (not in the air), since toe changes depending on the set (ride height) of the front wheels. Bump Steer Because the tie rods are at an angle, anytime the wheel moves up or down the tire will "turn" a little bit, because of the angle change of the tie rod. It's normally called "Bump Steer" because it affects cars that hit bumps. In our case we aren't hitting bumps, but the equivalent is happening when the front of the car is going up and down due to acceleration, gearshift change, and the action that results from hitting the brakes when slowing down. Std Beetles and Ghias are an even worse situation than Superbeetles because the tie rods are different lengths on the left compared to the right (Superbeetles have equal length tie rods). The amount of drop/raise from the steering box arm to the spindle hole is the same, so the angle of the tie rods is different on each side. What this means is that as the car goes higher and lower in the front, the wheels "steer" themselves at different rates. The Bump Steer problem is made even worse on VW's that have been lowered a lot without drop spindles, and/or cars that have narrowed axle beams (which makes the already short left tie rod even shorter). These situations cause extreme tie rod angles, which WILL create a bump steer problem. It's most prevalent just off the starting line since the front tires just barely touch the ground, and usually one tire lifts before the other and this can steer the car without the driving turning the steering wheel. The problem can be reduced by relocating the tie rod ends to the other side of the spindle mount with a Bump Steer Kit; this kit moves the tie rod ends to the bottom of the spindle, instead of the top, which reduces the tie rod angle. |
LhYnxz- Site Administrator
- Number of posts : 485
Age : 44
Location : Bayamon, PR
Reputation : 0
Points : 30
Registration date : 2007-12-01 -
Drag Racing Suspension and Setup for Type 1 pt2
by LhYnxz Thu Nov 27, 2008 3:54 pm
Step-by-step
Drag Car Set up
We'll begin with the setup
on a slower car, and work our way faster, which is also a good progression
from a driver's perspective, since not everyone just buys a 9sec Turbo
car and takes it out, we want to work our way up gaining experience
along the way. The best description we have heard of "11s"
in a VW is that it feels "violent" compared to other cars.
11 sec in a short wheelbase VW is like 9 sec in a Camaro, because our
cars are so light and have that short wheelbase. It's a
handful! We recommend that you ease your way into going fast: Get experience.
There aren't too many faster ways to hurt yourself or your nice car
than to go straight from an 18 second beetle to one that runs 11s!
Since you are going
to be driving your car hard, the stock engine mount arrangement is not
going to cut it, even if you are running with a stock engine. The problem
is the engine and transaxle are "hanging" off the rear torsion
housing, on the end of the frame horns. Those look quite stiff, but
I assure you they are not. The result is that the engine and transmission
can "springboard" the end of the frame horns, this loads and
unloads the chassis and tires, resulting in a violent oscillation called
"wheel hop". There are 2 ways to prevent this: We'll start
with the least expensive.
Option 1: Install a "Traction
Bar". This is a thick steel tube that supports the weight of the
engine (at the rear), and keeps the engine/transmission assembly from
flexing down. If it doesn't flex down, it won't bounce up! These bars
are simple in their design, but they work well, and bolt to the body
of the car. I'll tell straight away that if the Traction bar is under
$40, it's not strong enough for drag racing! Many companies are selling
bars cheap by making them cheap -- making them out of thin tubing which
flexes too much to offer appropriate support. Get a good bar! We recommend
MINIMUM 1 1/2" Square, .125" wall tubing. Most of the cheap
ones are 1" and chrome, you may as well tape the box to your engine!
Keep in mind that you can't use a traction bar if the car is all hacked
up (superlight) or rusted out, because you won't get much support because
of body flex under load. The other drawback to a traction bar is that
they tend to be in the way of the oil lines (from your full flow oiling
system), and exhaust system, and you have to take it off every time
you remove the engine. We have successfully solved this problem by installing
the traction bar at the back of the frame horns (instead of the engine).
This is not commonly known, but it works!
Option 2: For those of you
who have deeper pockets, install a Kafer Cup Brace, TG Brace, etc. These
devices support the weight of the engine and transmission from the end
of the transmission, right near the end of the frame horns. Be careful
when choosing this device, some are not engineered properly, instead
of being designed solely for the job at hand, were designed to be easy
to make -- and so many of the ones on the market have limited strength.
The downrods on this device should be triangulated at the intersection,
a downrod should NOT meet the crossbar somewhere other then the VERY
END.
Option 3: The third choice
is to tie the transmission support into the rollcage or chassis. Some
rollcages (like ours) have a kit to tie it right in, other guys weld
bars from the frame horns to the shock towers, etc. Anything that keeps
the frame horns from flexing down and up will work. Just remember to
make it so you can still remove the transmission if you have to!
In the front of the transmission,
the nosecone is getting yanked UP by the torque of the engine and traction.
This torque can break the front transmission mount, or the nosecone
of the transmission. To solve this potential issue, install an Intermediate
Transmission Mount, they take 30 minutes to install, and will keep the
transmission in place, without adding any additional noise to the car.
Another related item are the transmission mounts. There are 2 different
designs of rear mounts, 72 and older, and 73 and newer. The 73 and newer
mounts are about twice as thick, for a nice quiet ride. The problem
with being 2x as thick, is they are 4X as flexible, and because of this
they don't cut it for drag racing. The amount of engine movement at
speed causes the left intake manifolds to hit the engine compartment,
and as a result, 73 and newer owners will find that the left hand intake
manifold constantly comes loose and leaks air. You are just gonna have
to suck it up and replace the stock 73+ rubber mounts to the earlier
style mount, and while you are at it, you should also upgrade to urethane
mounts. 72 and older German rear mounts work fine until you are in the
high 12 sec range, but at that point the mounts are too compressible
and soft to hold up under the stress. I ran HD early rubber mounts in
my car and had wheel hop (bad case of it too). I had everything, Urethane
Spring Plate Bushings, Intermediate Mount, Kafer Cup Brace, and STILL
had wheel hop so bad my electrical wires on the engine and taillights
disconnected when I launched the car -- it was ugly! Though there was
no way to actually check it, I assumed the cause was the rubber mounts
compressing on the launch, and once I went to urethane it launched as
smooth as anything with no wheelhop at all. You can use urethane, or
solid mounts. Solid mounts are loud, because they transmit all engine
and transmission noise into the car. With solid transmission mounts
it's not uncommon for fender bolts and nuts to vibrate loose, so if
it's a real driver just get urethane -- they are quiet.
It's worth noting that rear
mount changes require the engine to come out, so plan this and clutch
work at the same time. And don't forget to properly setup the Bowden
Tube between the transmission and chassis. These keep tension on the
clutch cable constant, even as the engine and transmission move around
a bit. If the Bowden tube is mis-adjusted or missing, you can have a
bad case of wheel hop or clutch chatter (when the clutch is engaged
and disengaged due to torque, regardless of the state of your clutch
foot).
Next item: unless you have
changed them yourself or KNOW they have been changed (no guessing or
assumptions), you need to replace the torsion bar grommets (aka Spring
Plate Grommets). I can guarantee you that the stock ones are shot. There
is an inner and outer grommet on each side. These "center"
the spring plate in the torsion housing, and provide a "fixed pivot"
for the spring plate (well, at least it's supposed to be "fixed").
The problem with worn out grommets is that they allow the spring plate
to move up and down, and worse yet --fore and aft, which changes the
toe on the rear end of the car! The care will go toe-in under acceleration,
then toe-out when you let off the gas. It's really dangerous to have
a car steer itself when you are trying to go in a STRAIGHT LINE, depending
on how much your foot is on the gas! So, moral of the story?? Replace
the bushings! If you've ever had the opportunity to drive a forklift,
you'll know what I'm talking about. Forklift's steer from the back (like
a VW with worn out springplate bushings), and it's a handful at speed!
We recommend replacing the stock rubber grommets with urethane once
you get into the 12-13 second range. Proper installation of the urethane
bushings is covered in our product instructions when the product is
purchased, so I won't discuss it here, but you do not just "throw
them in", there is a little prep work to doing it right. If you
have an IRS rear suspension, you also need to replace the "Diagonal
Arm Grommets", again with urethane versions. Urethane is much harder
and stiffer than rubber, so it keeps the suspension components where
they are supposed to be, even under a lot more load (power). Stock rubber
components are fine for stock power, but they are too soft, compressible,
and elastic for higher loads; that's why you should use urethane when
you start going faster! When you REALLY start getting fast (11s or quicker)
you can install solid or "needle bearing" bushings in there.
Now onto the rear alignment.
The rear suspension is where many VW racers get into trouble!
Rear Toe; the holes where
the spring plates and diagonal arms bolt together are all slotted, so
you can move the wheel fore/aft to adjust the rear wheel toe. It's VERY
important to make sure that the toe is correct, AND that they are both
even on both sides! if they aren't even, the car can "crab"
moving diagonally down the track, with the back end of the car off to
one side of the front, even if the toe is correct! It's actually humorous
to me how many NEW PICKUPS have a mis-aligned rear axle, they crab all
the time (start looking for it). So use a fixed reverence point like
a torsion housing bolt (lower rear for example), and make sure they
are EXACTLY THE SAME. You may have to grind the spring plate slots a
little "longer" to get the correct adjustment; this is a perfectly
acceptable way to make your adjustments; just make sure you aren't compensating
for something else worn or bent somewhere else!
Drag Car Set up
We'll begin with the setup
on a slower car, and work our way faster, which is also a good progression
from a driver's perspective, since not everyone just buys a 9sec Turbo
car and takes it out, we want to work our way up gaining experience
along the way. The best description we have heard of "11s"
in a VW is that it feels "violent" compared to other cars.
11 sec in a short wheelbase VW is like 9 sec in a Camaro, because our
cars are so light and have that short wheelbase. It's a
handful! We recommend that you ease your way into going fast: Get experience.
There aren't too many faster ways to hurt yourself or your nice car
than to go straight from an 18 second beetle to one that runs 11s!
Since you are going
to be driving your car hard, the stock engine mount arrangement is not
going to cut it, even if you are running with a stock engine. The problem
is the engine and transaxle are "hanging" off the rear torsion
housing, on the end of the frame horns. Those look quite stiff, but
I assure you they are not. The result is that the engine and transmission
can "springboard" the end of the frame horns, this loads and
unloads the chassis and tires, resulting in a violent oscillation called
"wheel hop". There are 2 ways to prevent this: We'll start
with the least expensive.
Option 1: Install a "Traction
Bar". This is a thick steel tube that supports the weight of the
engine (at the rear), and keeps the engine/transmission assembly from
flexing down. If it doesn't flex down, it won't bounce up! These bars
are simple in their design, but they work well, and bolt to the body
of the car. I'll tell straight away that if the Traction bar is under
$40, it's not strong enough for drag racing! Many companies are selling
bars cheap by making them cheap -- making them out of thin tubing which
flexes too much to offer appropriate support. Get a good bar! We recommend
MINIMUM 1 1/2" Square, .125" wall tubing. Most of the cheap
ones are 1" and chrome, you may as well tape the box to your engine!
Keep in mind that you can't use a traction bar if the car is all hacked
up (superlight) or rusted out, because you won't get much support because
of body flex under load. The other drawback to a traction bar is that
they tend to be in the way of the oil lines (from your full flow oiling
system), and exhaust system, and you have to take it off every time
you remove the engine. We have successfully solved this problem by installing
the traction bar at the back of the frame horns (instead of the engine).
This is not commonly known, but it works!
Option 2: For those of you
who have deeper pockets, install a Kafer Cup Brace, TG Brace, etc. These
devices support the weight of the engine and transmission from the end
of the transmission, right near the end of the frame horns. Be careful
when choosing this device, some are not engineered properly, instead
of being designed solely for the job at hand, were designed to be easy
to make -- and so many of the ones on the market have limited strength.
The downrods on this device should be triangulated at the intersection,
a downrod should NOT meet the crossbar somewhere other then the VERY
END.
Option 3: The third choice
is to tie the transmission support into the rollcage or chassis. Some
rollcages (like ours) have a kit to tie it right in, other guys weld
bars from the frame horns to the shock towers, etc. Anything that keeps
the frame horns from flexing down and up will work. Just remember to
make it so you can still remove the transmission if you have to!
In the front of the transmission,
the nosecone is getting yanked UP by the torque of the engine and traction.
This torque can break the front transmission mount, or the nosecone
of the transmission. To solve this potential issue, install an Intermediate
Transmission Mount, they take 30 minutes to install, and will keep the
transmission in place, without adding any additional noise to the car.
Another related item are the transmission mounts. There are 2 different
designs of rear mounts, 72 and older, and 73 and newer. The 73 and newer
mounts are about twice as thick, for a nice quiet ride. The problem
with being 2x as thick, is they are 4X as flexible, and because of this
they don't cut it for drag racing. The amount of engine movement at
speed causes the left intake manifolds to hit the engine compartment,
and as a result, 73 and newer owners will find that the left hand intake
manifold constantly comes loose and leaks air. You are just gonna have
to suck it up and replace the stock 73+ rubber mounts to the earlier
style mount, and while you are at it, you should also upgrade to urethane
mounts. 72 and older German rear mounts work fine until you are in the
high 12 sec range, but at that point the mounts are too compressible
and soft to hold up under the stress. I ran HD early rubber mounts in
my car and had wheel hop (bad case of it too). I had everything, Urethane
Spring Plate Bushings, Intermediate Mount, Kafer Cup Brace, and STILL
had wheel hop so bad my electrical wires on the engine and taillights
disconnected when I launched the car -- it was ugly! Though there was
no way to actually check it, I assumed the cause was the rubber mounts
compressing on the launch, and once I went to urethane it launched as
smooth as anything with no wheelhop at all. You can use urethane, or
solid mounts. Solid mounts are loud, because they transmit all engine
and transmission noise into the car. With solid transmission mounts
it's not uncommon for fender bolts and nuts to vibrate loose, so if
it's a real driver just get urethane -- they are quiet.
It's worth noting that rear
mount changes require the engine to come out, so plan this and clutch
work at the same time. And don't forget to properly setup the Bowden
Tube between the transmission and chassis. These keep tension on the
clutch cable constant, even as the engine and transmission move around
a bit. If the Bowden tube is mis-adjusted or missing, you can have a
bad case of wheel hop or clutch chatter (when the clutch is engaged
and disengaged due to torque, regardless of the state of your clutch
foot).
Next item: unless you have
changed them yourself or KNOW they have been changed (no guessing or
assumptions), you need to replace the torsion bar grommets (aka Spring
Plate Grommets). I can guarantee you that the stock ones are shot. There
is an inner and outer grommet on each side. These "center"
the spring plate in the torsion housing, and provide a "fixed pivot"
for the spring plate (well, at least it's supposed to be "fixed").
The problem with worn out grommets is that they allow the spring plate
to move up and down, and worse yet --fore and aft, which changes the
toe on the rear end of the car! The care will go toe-in under acceleration,
then toe-out when you let off the gas. It's really dangerous to have
a car steer itself when you are trying to go in a STRAIGHT LINE, depending
on how much your foot is on the gas! So, moral of the story?? Replace
the bushings! If you've ever had the opportunity to drive a forklift,
you'll know what I'm talking about. Forklift's steer from the back (like
a VW with worn out springplate bushings), and it's a handful at speed!
We recommend replacing the stock rubber grommets with urethane once
you get into the 12-13 second range. Proper installation of the urethane
bushings is covered in our product instructions when the product is
purchased, so I won't discuss it here, but you do not just "throw
them in", there is a little prep work to doing it right. If you
have an IRS rear suspension, you also need to replace the "Diagonal
Arm Grommets", again with urethane versions. Urethane is much harder
and stiffer than rubber, so it keeps the suspension components where
they are supposed to be, even under a lot more load (power). Stock rubber
components are fine for stock power, but they are too soft, compressible,
and elastic for higher loads; that's why you should use urethane when
you start going faster! When you REALLY start getting fast (11s or quicker)
you can install solid or "needle bearing" bushings in there.
Now onto the rear alignment.
The rear suspension is where many VW racers get into trouble!
Rear Toe; the holes where
the spring plates and diagonal arms bolt together are all slotted, so
you can move the wheel fore/aft to adjust the rear wheel toe. It's VERY
important to make sure that the toe is correct, AND that they are both
even on both sides! if they aren't even, the car can "crab"
moving diagonally down the track, with the back end of the car off to
one side of the front, even if the toe is correct! It's actually humorous
to me how many NEW PICKUPS have a mis-aligned rear axle, they crab all
the time (start looking for it). So use a fixed reverence point like
a torsion housing bolt (lower rear for example), and make sure they
are EXACTLY THE SAME. You may have to grind the spring plate slots a
little "longer" to get the correct adjustment; this is a perfectly
acceptable way to make your adjustments; just make sure you aren't compensating
for something else worn or bent somewhere else!
LhYnxz- Site Administrator
- Number of posts : 485
Age : 44
Location : Bayamon, PR
Reputation : 0
Points : 30
Registration date : 2007-12-01 -
Drag Racing Suspension and Setup for Type 1 pt3
by LhYnxz Thu Nov 27, 2008 3:58 pm
Shoot for 1/16-1/8" rear toe in for a nice stable (safe) ride.
IRS: Things are relatively
easy because the wheel camber and toe change little throughout the range
of rear suspension travel. The first thing to look at is rear wheel
Camber. If the rear tires are "In" at the top, there's something
wrong. Either the diagonal arm bushings, or the spring plate bushings,
are bad (but you should have already replaced these, remember?), or
the diagonal arms are actually tweaked or bent. This is not uncommon,
especially given the # of miles and years these cars have been driven
before we got the car. The solution is to either get some non-tweaked
arms, or a backyard trick is to put the left side diagonal arm on the
right, and the right side diagonal arm on the left; this will require
that you cut off and re-weld the lower shock mounts on each, and you'll
have to unbolt and bolt up the rear brake assemblies, but it does work
and will correct the camber problem.
Swing Axle: The Swing Axle
rear suspension is a simpler design, but along with this simplicity
come a couple inherent problems. The swing axle rear suspension is jointed
at the transmission, so that as the wheel moves up, the top tips in
more then the bottom does (camber change). The spring plate is pivoted
at the torsion bar grommets, so as the wheel moves up and down, the
Toe changes too. Swing Axle rear suspensions have HUGE changes in rear
wheel alignment throughout the wheel travel, so you really have to understand
what's going on, and how to prevent problems.
Think about the Launch: the
rear end squats, and the tires go to negative camber (top in) AND toe
in (as the wheel moves all the way up). During the gear shift or if
you let up off the gas (hit the brakes after the finish line), the rear
unloads and the camber goes + while the toe gets less then more! Remember,
the toe is at it's minimum when the spring plate is level (straight
back). As the wheel is above and below this, the toe goes more negative.
So about the only things
you can adjust on a swing axle are the spring rates, shock rates, toe,
but the secret is to LIMIT the wheel travel, since this limits the amount
of CHANGE the rear alignment is doing, this will become more clear as
we discuss it. To set the toe, scribe a line down the middle of both
rear tires. This is easily done by jacking up the car and putting a
stand under the end of each axle to ensure the axles are level (not
rear tires hanging). Now spin the tire (or run it in gear) and use a
pointed metal scribe to cut a thin shallow line into the tire (Chalk
or pencil is too fat to be accurate). Do both tires. These are your
reference lines, and it's much more accurate then using the lip of the
wheel (which may be bent, and bent wheels are a lot more common then
people realize, so NEVER EVER use the wheel for reference). Now measure
the toe, AND measure the distance from the wheel to something on the
CAR to check that both sides are the same. Make sure the car is on the
ground, and roll it back 10' then forward 10' to set the suspension
back to normal. (many swingaxle cars will "jack" the rear
if you roll backwards, so the last motion should be rolling forwards
prior to measuring). And always make sure the tape measure is parallel
to the ground, and measure the distance from line to line in front,
then the rear of the rear tires. Because the tape measure ends are often
loose or bent, we recommend starting your measurement from "1"
every time for repeatability. Now the difference between front tire
line and the rear tire line is your Toe in/out. Adjust both sides equally
to change toe; you simply push the axles forward (in their slots) to
get more toe-in, pull them backwards to get toe-out. If you don't have
enough toe in, that's not an excuse to just shove the axle tube forwards
and tighten it down, you may have to have to break out the die grinder
to lengthen the slots in the springplates to get the alignment right
(stock slots are often too short and limit your adjustment), don't be
lazy do it. After tightening the 6 springplate bolts, recheck (because
they move, and you need to check it). You should aim for 1/16-1/8"
rear toe IN; this is critically important! There are others that feel
that swingaxle VWs should run Toe-out in the rear, but I feel this is
very dangerous and a huge mistake (unless you like sliding on you roof
or gripping the seat cushion with your @$$).Guys who run Auto-X or slalom
in swing axle VWs often run rear Toe-out so the back end of the car
swings around faster. And as Mark Herbert once remarked, " Slalom
guys use toe out for the rear suspension. If you want to go straight
I think it's in your best interest to not use slalom alignment".
:-)
I agree! Mark has a funny way of putting things, LOL. So setup the rear
toe for 1/16-1/8" Toe-IN. Once you have this setting, we recommend
you mark or scribe the location of the axle tube ends on the spring
plates, if you have to change the transmission you'll know they'll be
real close prior to re-checking the alignment.
Back to the front for further setup, this part is easy. In a slower
car, there is little weight transfer because the car accelerates so
slowly. It's important to realize that the drive wheels are in the back.
It's also important to understand that the more force on the rear tires,
the more grip they'll have. While it sounds simple, think further. The
ideal situation is where the weight of the car is being supported ONLY
BY THE REAR WHEELS (wheelie), that's how you get the highest possible
traction, and accelleration during your launch. If your wheels spin,
you need to get more weight on the rear tires. Another way of looking
at it is you need to get weight OFF the front tires. One common method
to do this is to get the front end UP. Lowering the front of the car
looks great, but it really hurts your traction during accelleration,
especially with stiff (stock) torsion leaves. The 2 ways to accomplish
this are softer springs in the front, and some 90/10 shocks in the front.
90/10 shocks have almost 0 resistance to extension, but are very stiff
on compression. So they allow the front of the car to lift, then keep
it up, which helps put weight on the rear tires. Besides 90/10s, you
can soften the spring rate in the front. Some folks remove torsion leaves
(put in dummy leaves where the grub screws secure the leaves in place
to prevent leaf pull-out or a torsion arm falling off the car!) to soften
the spring rate in the front, which lowers the front of the car AND
more importantly gets some much needed weight transfer (up and down
motion), this is great for traction on the starting line and first 330'
of the race.
As the car gets faster, the need for this "weight transfer assistance"
goes away, and you'll eventually need to take the 90/10s back off the
front, since the car will accelerate hard enough to pull the wheels
without 90/10s, and you may have to go back to stock spring rate in
the front if the wheelies are too high. Typically the change away from
the 90/10s back to stock front shocks will be in the high 11 to low
12 sec range. If you leave them on the wheelies will be too high, and
this slows down the 60' (launch) and is flat out scary (and dangerous
if the car doesn't go straight, you can't see the track!). Ideally you
want a 6-18" wheelie in the front, and you won't even feel the
front end lift or come back down, your friends will let you know when
you get back to the pits! ;-)
If you do a wheelie, do NOT get scared and get off the gas (lift), the
front end will slam down and you could end up with a bunch of broken
and bent car parts!
If the car is lifting the wheels beyond the 18" height, you need
to stiffen the front end up by stiffer shocks or more spring rate in
the front. Wheelie bars are another option. Do not set wheelie bars
to keep the front on the ground, just adjust them to keep the front
end from going too high (remember, we WANT the wheelie). If you have
a choice longer wheelie bars are always better then short bars, they
don't unload the rear tires as much. Another tip on Wheelie Bars, make
sure they wind up like a spring. You do not want to hit the wheelie
bars hard, it should wind up and down as you come on and off the bars,
for a smooth transfer. Smooth is good.
Now on the other end of the track (top end), we discussed the importance
of caster in the front end. The simple act of letting off the gas and/or
hitting the brakes lifts the rear and drops the front of the car, which
changes the front caster, and rear camber/toe dramatically! This abrupt
change can make the car VERY squirrelly. So we are going to make sure
we adjust things so this "problem" is minimized.
As the car gets faster and
faster, it's going to "launch" harder. We WANT it to Launch
hard, but the harder it launches, the more load it's putting on the
shocks and torsion bars. What you do not want to do is slam down onto
your rear snubbers; because if this happens, it will shock-load the
transmission, possibly breaking parts, and if it doesn't break the gearbox
it will compress the tires and then bounce up off of them, which then
unloads them on the rebound, and then the tires spin since they are
off the ground or have almost no weight on them. Ideally you want to
use the available rear suspension travel, but not "bottom out hard"
on the snubbers.
What some folks do is keep the rear of the car fairly low, but then
use Bus Snubbers in the rear, to act like a STIFF SPRING that prevents
compressing. If you do this, you have to be careful that you don't have
a lot of gap before you hit the snubber, because as we have mentioned
before if you have a lot of gap and hit it hard, you'll be phoning your
transmission guy tomorrow (BANG). So some guys use the stock rear torsions
and bus snubbers, with about 1 finger thickness gap off the snubber.
The bus snubbers are more progressive then the bug ones, and also taller
to prevent the huge squat which creates that negative camber situation.
If you get a lot of negative camber, you'll only be using around 2"
of those 6" slicks. A lot of negative camber during the launch
is a no-no, keep the tires as flat as possible on the track. IRS doesn't
have this issue with camber, but you do have to worry about hitting
the snubber hard, because that can break your transaxle or your CV Joints.
IRS: Things are relatively
easy because the wheel camber and toe change little throughout the range
of rear suspension travel. The first thing to look at is rear wheel
Camber. If the rear tires are "In" at the top, there's something
wrong. Either the diagonal arm bushings, or the spring plate bushings,
are bad (but you should have already replaced these, remember?), or
the diagonal arms are actually tweaked or bent. This is not uncommon,
especially given the # of miles and years these cars have been driven
before we got the car. The solution is to either get some non-tweaked
arms, or a backyard trick is to put the left side diagonal arm on the
right, and the right side diagonal arm on the left; this will require
that you cut off and re-weld the lower shock mounts on each, and you'll
have to unbolt and bolt up the rear brake assemblies, but it does work
and will correct the camber problem.
Swing Axle: The Swing Axle
rear suspension is a simpler design, but along with this simplicity
come a couple inherent problems. The swing axle rear suspension is jointed
at the transmission, so that as the wheel moves up, the top tips in
more then the bottom does (camber change). The spring plate is pivoted
at the torsion bar grommets, so as the wheel moves up and down, the
Toe changes too. Swing Axle rear suspensions have HUGE changes in rear
wheel alignment throughout the wheel travel, so you really have to understand
what's going on, and how to prevent problems.
Think about the Launch: the
rear end squats, and the tires go to negative camber (top in) AND toe
in (as the wheel moves all the way up). During the gear shift or if
you let up off the gas (hit the brakes after the finish line), the rear
unloads and the camber goes + while the toe gets less then more! Remember,
the toe is at it's minimum when the spring plate is level (straight
back). As the wheel is above and below this, the toe goes more negative.
So about the only things
you can adjust on a swing axle are the spring rates, shock rates, toe,
but the secret is to LIMIT the wheel travel, since this limits the amount
of CHANGE the rear alignment is doing, this will become more clear as
we discuss it. To set the toe, scribe a line down the middle of both
rear tires. This is easily done by jacking up the car and putting a
stand under the end of each axle to ensure the axles are level (not
rear tires hanging). Now spin the tire (or run it in gear) and use a
pointed metal scribe to cut a thin shallow line into the tire (Chalk
or pencil is too fat to be accurate). Do both tires. These are your
reference lines, and it's much more accurate then using the lip of the
wheel (which may be bent, and bent wheels are a lot more common then
people realize, so NEVER EVER use the wheel for reference). Now measure
the toe, AND measure the distance from the wheel to something on the
CAR to check that both sides are the same. Make sure the car is on the
ground, and roll it back 10' then forward 10' to set the suspension
back to normal. (many swingaxle cars will "jack" the rear
if you roll backwards, so the last motion should be rolling forwards
prior to measuring). And always make sure the tape measure is parallel
to the ground, and measure the distance from line to line in front,
then the rear of the rear tires. Because the tape measure ends are often
loose or bent, we recommend starting your measurement from "1"
every time for repeatability. Now the difference between front tire
line and the rear tire line is your Toe in/out. Adjust both sides equally
to change toe; you simply push the axles forward (in their slots) to
get more toe-in, pull them backwards to get toe-out. If you don't have
enough toe in, that's not an excuse to just shove the axle tube forwards
and tighten it down, you may have to have to break out the die grinder
to lengthen the slots in the springplates to get the alignment right
(stock slots are often too short and limit your adjustment), don't be
lazy do it. After tightening the 6 springplate bolts, recheck (because
they move, and you need to check it). You should aim for 1/16-1/8"
rear toe IN; this is critically important! There are others that feel
that swingaxle VWs should run Toe-out in the rear, but I feel this is
very dangerous and a huge mistake (unless you like sliding on you roof
or gripping the seat cushion with your @$$).Guys who run Auto-X or slalom
in swing axle VWs often run rear Toe-out so the back end of the car
swings around faster. And as Mark Herbert once remarked, " Slalom
guys use toe out for the rear suspension. If you want to go straight
I think it's in your best interest to not use slalom alignment".
:-)
I agree! Mark has a funny way of putting things, LOL. So setup the rear
toe for 1/16-1/8" Toe-IN. Once you have this setting, we recommend
you mark or scribe the location of the axle tube ends on the spring
plates, if you have to change the transmission you'll know they'll be
real close prior to re-checking the alignment.
Back to the front for further setup, this part is easy. In a slower
car, there is little weight transfer because the car accelerates so
slowly. It's important to realize that the drive wheels are in the back.
It's also important to understand that the more force on the rear tires,
the more grip they'll have. While it sounds simple, think further. The
ideal situation is where the weight of the car is being supported ONLY
BY THE REAR WHEELS (wheelie), that's how you get the highest possible
traction, and accelleration during your launch. If your wheels spin,
you need to get more weight on the rear tires. Another way of looking
at it is you need to get weight OFF the front tires. One common method
to do this is to get the front end UP. Lowering the front of the car
looks great, but it really hurts your traction during accelleration,
especially with stiff (stock) torsion leaves. The 2 ways to accomplish
this are softer springs in the front, and some 90/10 shocks in the front.
90/10 shocks have almost 0 resistance to extension, but are very stiff
on compression. So they allow the front of the car to lift, then keep
it up, which helps put weight on the rear tires. Besides 90/10s, you
can soften the spring rate in the front. Some folks remove torsion leaves
(put in dummy leaves where the grub screws secure the leaves in place
to prevent leaf pull-out or a torsion arm falling off the car!) to soften
the spring rate in the front, which lowers the front of the car AND
more importantly gets some much needed weight transfer (up and down
motion), this is great for traction on the starting line and first 330'
of the race.
As the car gets faster, the need for this "weight transfer assistance"
goes away, and you'll eventually need to take the 90/10s back off the
front, since the car will accelerate hard enough to pull the wheels
without 90/10s, and you may have to go back to stock spring rate in
the front if the wheelies are too high. Typically the change away from
the 90/10s back to stock front shocks will be in the high 11 to low
12 sec range. If you leave them on the wheelies will be too high, and
this slows down the 60' (launch) and is flat out scary (and dangerous
if the car doesn't go straight, you can't see the track!). Ideally you
want a 6-18" wheelie in the front, and you won't even feel the
front end lift or come back down, your friends will let you know when
you get back to the pits! ;-)
If you do a wheelie, do NOT get scared and get off the gas (lift), the
front end will slam down and you could end up with a bunch of broken
and bent car parts!
If the car is lifting the wheels beyond the 18" height, you need
to stiffen the front end up by stiffer shocks or more spring rate in
the front. Wheelie bars are another option. Do not set wheelie bars
to keep the front on the ground, just adjust them to keep the front
end from going too high (remember, we WANT the wheelie). If you have
a choice longer wheelie bars are always better then short bars, they
don't unload the rear tires as much. Another tip on Wheelie Bars, make
sure they wind up like a spring. You do not want to hit the wheelie
bars hard, it should wind up and down as you come on and off the bars,
for a smooth transfer. Smooth is good.
Now on the other end of the track (top end), we discussed the importance
of caster in the front end. The simple act of letting off the gas and/or
hitting the brakes lifts the rear and drops the front of the car, which
changes the front caster, and rear camber/toe dramatically! This abrupt
change can make the car VERY squirrelly. So we are going to make sure
we adjust things so this "problem" is minimized.
As the car gets faster and
faster, it's going to "launch" harder. We WANT it to Launch
hard, but the harder it launches, the more load it's putting on the
shocks and torsion bars. What you do not want to do is slam down onto
your rear snubbers; because if this happens, it will shock-load the
transmission, possibly breaking parts, and if it doesn't break the gearbox
it will compress the tires and then bounce up off of them, which then
unloads them on the rebound, and then the tires spin since they are
off the ground or have almost no weight on them. Ideally you want to
use the available rear suspension travel, but not "bottom out hard"
on the snubbers.
What some folks do is keep the rear of the car fairly low, but then
use Bus Snubbers in the rear, to act like a STIFF SPRING that prevents
compressing. If you do this, you have to be careful that you don't have
a lot of gap before you hit the snubber, because as we have mentioned
before if you have a lot of gap and hit it hard, you'll be phoning your
transmission guy tomorrow (BANG). So some guys use the stock rear torsions
and bus snubbers, with about 1 finger thickness gap off the snubber.
The bus snubbers are more progressive then the bug ones, and also taller
to prevent the huge squat which creates that negative camber situation.
If you get a lot of negative camber, you'll only be using around 2"
of those 6" slicks. A lot of negative camber during the launch
is a no-no, keep the tires as flat as possible on the track. IRS doesn't
have this issue with camber, but you do have to worry about hitting
the snubber hard, because that can break your transaxle or your CV Joints.
LhYnxz- Site Administrator
- Number of posts : 485
Age : 44
Location : Bayamon, PR
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Points : 30
Registration date : 2007-12-01 -
Drag Racing Suspension and Setup for Type 1 pt4
by LhYnxz Thu Nov 27, 2008 3:59 pm
Low budget racers will typically "preload" the rear torsion
bars, which makes them stiffer, and it does in fact work for the launch,
the problem is when they shift or let up off the gas, there's all that
preload that will lift the back end up on the top end (which reduces
front caster, and increases the rear toe/camber problem, not to mention
aerodynamics!). Remember the softer the springs, the MORE TRAVEL you
are going to have from launch to lift! It's the exact opposite of what
many folks assume, they think a stiff spring will move the suspension
more (because it's pushing so hard), but if you think about what an
infinite spring rate does (no spring, solid mounted suspension), it
has 0 travel. The softest springs have the most travel, those are the
guys that have to worry about the top end of the track! Stiffer torsion
bars in the back stabilize the car at the top end when you hit the brakes
or get off the gas because the rear doesn't move as much to unload those
stiff torsion bars.
Now if you use stock sized rear torsion bars with increased pre-load,
a solution to unloading the rear is to use Limit Straps. Limit Straps
are nylon straps (some people use lengths of chain) that prevent the
rear wheels from dropping down, even though the torsion bars are preloaded
beyond a normal amount. Limit straps are typically "taught"
before the spring plate hits the stop. You can twist the limit strap
to make it "shorter" for minor length adjustments. This needs
to be checked periodically, since limit straps do stretch with use,
eventually rendering them ineffective and requiring re-adjustment.
If you want to "do it
right" AND have deeper pockets ($$$), the obvious solution is larger
rear torsion bars. These are not needed until the car gets faster, typically
high 11s to low 12s. We know there are guys going faster on stock bars,
but that's not the point. The beauty of larger rear torsion bars is
they are stiffer which prevents bottoming out, but they also accomplish
this without having to be preloaded! On my car (for example; a 64' Beetle
with short axles), I elected to use a 28mm torsion bar, and have removed
the rear snubbers, since the bars are so stiff I wouldn't hit them anyways.
I have it setup so that my spring plates JUST slip over the spring plate
stop, with 0 preload. This prevents the "high-jacking" effect
of hitting the brakes at the top end of the track, but has enough spring
to prevent bottoming. I have Limit Straps on there too, but they are
fairly loose. If the limit straps are too tight, the wheels can't "drop"
and if you hit a bump the car can go airborne, NOT GOOD. So you want
some wheel travel to suck up the bumps and follow the dips, when you
are traveling at speed. As we have stated before, you can crash with
too much or not enough suspension travel, you want to find that sweet
spot. FYI, you can measure and track how much squat the car gets by
putting a snug (but not tight) collar on the shaft of the rear shock
(a grommet with a slit in it, wrapped with a hose clamp also works).
After a pass, take a look at the collar and see how far it moved, this
is how much the car squatted since the bottom of the collar was sitting
on the shock body. I'd check both sides to see that the car is squatting
equally, and just slip them back down to check the next run.
Now larger rear torsion bars
have an increased spring rate, which is why we bought them in the first
place! But the problem with the stiffer springrate is that now the stock
valved rear shocks are inadequate (aka: TOO SOFT) to control the harder
launch and rebound from those stronger torsion bars; So the solution
are some rear drag shocks. These typically come in 2 forms; Steel Bodied,
and Aluminum Bodied. The Aluminum ones are obviously lighter, but their
advantages go further then Weight Weenie status! Typical Steel bodied
shocks have 3 adjustments; 40/60, 50/50, and 60/40. This is a limited
range, and to ADJUST them you have to fully compress them, which means
unbolting the top or bottom of the shock, adjusting, then bolting it
back up. Lotsa' fun! The nice thing about the aluminum adjustable shocks
is they usually have an readily accessible knob, with a range of about
30-40 settings! A LOT more adjustability, and you can do this "on
the car" in about 15 seconds. The stronger shocks is why making
the jump to larger torsion bars is not as cheap as just buying the torsion
bars, because you also need to pony up for some stronger shocks!
Another tip to be aware of.
If your car is fast (mid 12s or faster), you can have the correct
alignment, bigger rear torsion bars, urethane grommets, and still have
a problem with the car being very erratic off the line, and it's often
due to the stock spring plates! They are not very thick, and they can
actually flex significantly during the initial launch (especially with
good traction and big-power), which REALLY changes the rear toe! Bigger
(Thicker) rear spring plates (adjustable or not) will prevent this springboard
effect present with the thin stock springplates. One tip to check is
to paint a line from fore/aft on the spring plate with a "brittle"
paint; let it dry and then make a run. When you get back to the pits
check the paint; if the paint is cracked, I think it's safe to assume
the spring plates are flexing a little more then you'd like, and it's
time for some HD spring plates! Old Timers knew about this problem,
they used to double up spring plates and weld them to stiffen the stockers
up, before HD ones were available. This is often the one change that
can transform an unpredictable car to one that goes straight with ease.
The other thing I do to tune the car is not use too much clutch! I feel
that most VWs are over-clutched. The problem with this is the clutch
is WAY stronger then the engine's power output, which to me is really
stupid. Why do you need 270lb/ft of holding power if the engine makes
180lb/ft of torque? I'll tell you why, so you can break stuff! You do
not need a Stage II KEP if you are running 12s or slower in the 1/4
mile, just run a Stage I and a stock disc, or for a little more holding
power use a Daikin or Copperhead (I use a Copperhead). Use the Hercules
Clutch Setups if you want to break the R&P, or spin the flywheel
off the crank. When guys go to 7k and drop the clutch with the Big Setup,
the engine is connected to the wheels RIGHT NOW, and this breaks stuff.
Another common sight is a guy doing a huge wheelie and barely go anywhere
(the most common occurrence, though this does "look great"
in the pictures, but in person it's a joke), then the car finally starts
to move if the transaxle or axles didn't lay down on the starting line
(BANG!). I like SOFT clutch setups, and one huge advantage to this is
that if the track is super sticky, my car launches the exact same, since
the clutch slips a little bit, and I also do not grenade transaxles!
Yes it is true that you will change clutch discs more often, but it's
not unusual to get 200 passes out of the disc before having to change
the disc, and I would rather change 5 clutch discs then 1 transaxle
LOL. My transaxles live a long time because they are not abused, and
the biggest advantage is that the car LAUNCHES THE EXACT SAME regardless
of what track I am racing at. Talk about lazy-man's setup, I don't even
have to change anything if I go to a sticky track, the clutch slips
and the car launches the same, even if I'm at a gearbox-bustin' NHRA
track with a ton of traction compound. I do give up .05sec or so in
my 60' time by running soft, but in return I get to drink a beverage-of-choice
between rounds. You can be a sport and bring a cold one to the hero
that's got his setup on KILL and is changing his gearbox between rounds
LOL. It actually works to your advantage if your rivals see you sitting
in the shade hanging out while they are scrambling to fix something.
It really screws with their head if they have to race you, they are
catching up just to make the next round, you are already ready. Another
tip: if you use a lot of slip in the clutch, it can get pretty hot,
especially after consecutive passes. If the car starts to launch different
in later rounds then earlier ones, the clutch may be getting hot, and
it doesn't have a chance to cool off between rounds. What some guys
do is cut a couple holes in the transmission bellhousing, and between
rounds slip a leaf blower into one of the holes, to cool off the clutch
to get the consistency back! ;-)
Tire Pressure: If you have street tires (street radials), you'll run
24-28psi in your rear tires, and 20psi in the front tires. If you have
slicks, you'll use a much lower tire pressure. I recommend starting
with around 17psi in the rear for Slicks or DOTs. If they spin, try
to increase the burnout duration, or drop the tire pressure 1-2psi until
you find the sweet spot. Remember that drag racing is a series of compromises,
what works on the launch often hurts you on the other end of the track,
and this is the case with rear tire pressure. Lower pressures give more
"hook" for a good launch, but can get wiggly and loose at
the top end, since there is no pressure to keep the sidewall stiff and
straight. High pressures are stable up top but more slippery on the
starting line. The tire pressure you need will depend on the weight
of the car, and the width of the tire. Heavier cars need more tire pressure
then lighter cars. A buggy may use 8psi, your heavy sedan may use 18psi,
with the same tire! 95% of VW applications use a 6" slick, I'd
start with 17psi in these, and they are good down to around 12psi. If
you need less then 12psi, the tires are either too cold, too OLD (rock
hard and slippery), or something else is wrong with the suspension setup.
If you need more then 20psi, the tires are likely too much for your
car (too wide). Be aware that a lot of these guidelines depend on the
track preparation. Many smaller tracks have to mow the grass on the
starting line on Friday afternoon prior to racing, while the Big Time
NHRA tracks like Vegas will suck your shoe right off your foot if you
happen to walk up there. So obviously there are huge differences in
track prep, and you have to learn to adjust your routine and your setup
prior to the race you are going to attend. If the track is sticky, soften
up the rear shocks and air up the rear tires a bit and see how the car
does. The amount of adjusting you'll have to do once the car is properly
setup won't be much. Many folks adjust tire pressures expecting to do
all the tuning with the tires, when they should be adjusting the shocks
or suspension not tire pressures. You will have a range of 3-4psi you'll
be working with at the various tracks you may attend, if you just frequent
one track you usually won't have to change much at all, since the track
will be as good (or as bad) most of the time you show up.
The final issue to worry about is the top end aerodynamics. A VW Bug
body is shaped like a WING for crying out loud! Flat on the bottom,
and curved on the top, and to make matters worse the front end is light.
If you address the alignment and suspension issues as discussed, you'll
have no problems up to around 110mph provided you don't have some unexpected
breakage or hit a slick spot (oil) on the track. Once you hit the 110mph
zone it's time to add a rear spoiler to reduce the lift created by this
airspeed. Even the old Herrod Helpers will help a good bit over 100mph,
or you can go crazy with a full on drag wing if you are really moving
(130+). Our Street Wing is for in between these 2 terminal speeds, and
it does keep the car straight and rubber side down.
We really hope this article helps you in setting up your car to be safe
at the track -- but don't be afraid to apply the principles and mods
to driving on the street. We have seen some street cars that were death
traps at 55mph, well under the speed limits in many areas. You can apply
these principles to make your street car the safest VW in the neighborhood.
Good luck, and let us know
if this information helped you setup your car!
bars, which makes them stiffer, and it does in fact work for the launch,
the problem is when they shift or let up off the gas, there's all that
preload that will lift the back end up on the top end (which reduces
front caster, and increases the rear toe/camber problem, not to mention
aerodynamics!). Remember the softer the springs, the MORE TRAVEL you
are going to have from launch to lift! It's the exact opposite of what
many folks assume, they think a stiff spring will move the suspension
more (because it's pushing so hard), but if you think about what an
infinite spring rate does (no spring, solid mounted suspension), it
has 0 travel. The softest springs have the most travel, those are the
guys that have to worry about the top end of the track! Stiffer torsion
bars in the back stabilize the car at the top end when you hit the brakes
or get off the gas because the rear doesn't move as much to unload those
stiff torsion bars.
Now if you use stock sized rear torsion bars with increased pre-load,
a solution to unloading the rear is to use Limit Straps. Limit Straps
are nylon straps (some people use lengths of chain) that prevent the
rear wheels from dropping down, even though the torsion bars are preloaded
beyond a normal amount. Limit straps are typically "taught"
before the spring plate hits the stop. You can twist the limit strap
to make it "shorter" for minor length adjustments. This needs
to be checked periodically, since limit straps do stretch with use,
eventually rendering them ineffective and requiring re-adjustment.
If you want to "do it
right" AND have deeper pockets ($$$), the obvious solution is larger
rear torsion bars. These are not needed until the car gets faster, typically
high 11s to low 12s. We know there are guys going faster on stock bars,
but that's not the point. The beauty of larger rear torsion bars is
they are stiffer which prevents bottoming out, but they also accomplish
this without having to be preloaded! On my car (for example; a 64' Beetle
with short axles), I elected to use a 28mm torsion bar, and have removed
the rear snubbers, since the bars are so stiff I wouldn't hit them anyways.
I have it setup so that my spring plates JUST slip over the spring plate
stop, with 0 preload. This prevents the "high-jacking" effect
of hitting the brakes at the top end of the track, but has enough spring
to prevent bottoming. I have Limit Straps on there too, but they are
fairly loose. If the limit straps are too tight, the wheels can't "drop"
and if you hit a bump the car can go airborne, NOT GOOD. So you want
some wheel travel to suck up the bumps and follow the dips, when you
are traveling at speed. As we have stated before, you can crash with
too much or not enough suspension travel, you want to find that sweet
spot. FYI, you can measure and track how much squat the car gets by
putting a snug (but not tight) collar on the shaft of the rear shock
(a grommet with a slit in it, wrapped with a hose clamp also works).
After a pass, take a look at the collar and see how far it moved, this
is how much the car squatted since the bottom of the collar was sitting
on the shock body. I'd check both sides to see that the car is squatting
equally, and just slip them back down to check the next run.
Now larger rear torsion bars
have an increased spring rate, which is why we bought them in the first
place! But the problem with the stiffer springrate is that now the stock
valved rear shocks are inadequate (aka: TOO SOFT) to control the harder
launch and rebound from those stronger torsion bars; So the solution
are some rear drag shocks. These typically come in 2 forms; Steel Bodied,
and Aluminum Bodied. The Aluminum ones are obviously lighter, but their
advantages go further then Weight Weenie status! Typical Steel bodied
shocks have 3 adjustments; 40/60, 50/50, and 60/40. This is a limited
range, and to ADJUST them you have to fully compress them, which means
unbolting the top or bottom of the shock, adjusting, then bolting it
back up. Lotsa' fun! The nice thing about the aluminum adjustable shocks
is they usually have an readily accessible knob, with a range of about
30-40 settings! A LOT more adjustability, and you can do this "on
the car" in about 15 seconds. The stronger shocks is why making
the jump to larger torsion bars is not as cheap as just buying the torsion
bars, because you also need to pony up for some stronger shocks!
Another tip to be aware of.
If your car is fast (mid 12s or faster), you can have the correct
alignment, bigger rear torsion bars, urethane grommets, and still have
a problem with the car being very erratic off the line, and it's often
due to the stock spring plates! They are not very thick, and they can
actually flex significantly during the initial launch (especially with
good traction and big-power), which REALLY changes the rear toe! Bigger
(Thicker) rear spring plates (adjustable or not) will prevent this springboard
effect present with the thin stock springplates. One tip to check is
to paint a line from fore/aft on the spring plate with a "brittle"
paint; let it dry and then make a run. When you get back to the pits
check the paint; if the paint is cracked, I think it's safe to assume
the spring plates are flexing a little more then you'd like, and it's
time for some HD spring plates! Old Timers knew about this problem,
they used to double up spring plates and weld them to stiffen the stockers
up, before HD ones were available. This is often the one change that
can transform an unpredictable car to one that goes straight with ease.
The other thing I do to tune the car is not use too much clutch! I feel
that most VWs are over-clutched. The problem with this is the clutch
is WAY stronger then the engine's power output, which to me is really
stupid. Why do you need 270lb/ft of holding power if the engine makes
180lb/ft of torque? I'll tell you why, so you can break stuff! You do
not need a Stage II KEP if you are running 12s or slower in the 1/4
mile, just run a Stage I and a stock disc, or for a little more holding
power use a Daikin or Copperhead (I use a Copperhead). Use the Hercules
Clutch Setups if you want to break the R&P, or spin the flywheel
off the crank. When guys go to 7k and drop the clutch with the Big Setup,
the engine is connected to the wheels RIGHT NOW, and this breaks stuff.
Another common sight is a guy doing a huge wheelie and barely go anywhere
(the most common occurrence, though this does "look great"
in the pictures, but in person it's a joke), then the car finally starts
to move if the transaxle or axles didn't lay down on the starting line
(BANG!). I like SOFT clutch setups, and one huge advantage to this is
that if the track is super sticky, my car launches the exact same, since
the clutch slips a little bit, and I also do not grenade transaxles!
Yes it is true that you will change clutch discs more often, but it's
not unusual to get 200 passes out of the disc before having to change
the disc, and I would rather change 5 clutch discs then 1 transaxle
LOL. My transaxles live a long time because they are not abused, and
the biggest advantage is that the car LAUNCHES THE EXACT SAME regardless
of what track I am racing at. Talk about lazy-man's setup, I don't even
have to change anything if I go to a sticky track, the clutch slips
and the car launches the same, even if I'm at a gearbox-bustin' NHRA
track with a ton of traction compound. I do give up .05sec or so in
my 60' time by running soft, but in return I get to drink a beverage-of-choice
between rounds. You can be a sport and bring a cold one to the hero
that's got his setup on KILL and is changing his gearbox between rounds
LOL. It actually works to your advantage if your rivals see you sitting
in the shade hanging out while they are scrambling to fix something.
It really screws with their head if they have to race you, they are
catching up just to make the next round, you are already ready. Another
tip: if you use a lot of slip in the clutch, it can get pretty hot,
especially after consecutive passes. If the car starts to launch different
in later rounds then earlier ones, the clutch may be getting hot, and
it doesn't have a chance to cool off between rounds. What some guys
do is cut a couple holes in the transmission bellhousing, and between
rounds slip a leaf blower into one of the holes, to cool off the clutch
to get the consistency back! ;-)
Tire Pressure: If you have street tires (street radials), you'll run
24-28psi in your rear tires, and 20psi in the front tires. If you have
slicks, you'll use a much lower tire pressure. I recommend starting
with around 17psi in the rear for Slicks or DOTs. If they spin, try
to increase the burnout duration, or drop the tire pressure 1-2psi until
you find the sweet spot. Remember that drag racing is a series of compromises,
what works on the launch often hurts you on the other end of the track,
and this is the case with rear tire pressure. Lower pressures give more
"hook" for a good launch, but can get wiggly and loose at
the top end, since there is no pressure to keep the sidewall stiff and
straight. High pressures are stable up top but more slippery on the
starting line. The tire pressure you need will depend on the weight
of the car, and the width of the tire. Heavier cars need more tire pressure
then lighter cars. A buggy may use 8psi, your heavy sedan may use 18psi,
with the same tire! 95% of VW applications use a 6" slick, I'd
start with 17psi in these, and they are good down to around 12psi. If
you need less then 12psi, the tires are either too cold, too OLD (rock
hard and slippery), or something else is wrong with the suspension setup.
If you need more then 20psi, the tires are likely too much for your
car (too wide). Be aware that a lot of these guidelines depend on the
track preparation. Many smaller tracks have to mow the grass on the
starting line on Friday afternoon prior to racing, while the Big Time
NHRA tracks like Vegas will suck your shoe right off your foot if you
happen to walk up there. So obviously there are huge differences in
track prep, and you have to learn to adjust your routine and your setup
prior to the race you are going to attend. If the track is sticky, soften
up the rear shocks and air up the rear tires a bit and see how the car
does. The amount of adjusting you'll have to do once the car is properly
setup won't be much. Many folks adjust tire pressures expecting to do
all the tuning with the tires, when they should be adjusting the shocks
or suspension not tire pressures. You will have a range of 3-4psi you'll
be working with at the various tracks you may attend, if you just frequent
one track you usually won't have to change much at all, since the track
will be as good (or as bad) most of the time you show up.
The final issue to worry about is the top end aerodynamics. A VW Bug
body is shaped like a WING for crying out loud! Flat on the bottom,
and curved on the top, and to make matters worse the front end is light.
If you address the alignment and suspension issues as discussed, you'll
have no problems up to around 110mph provided you don't have some unexpected
breakage or hit a slick spot (oil) on the track. Once you hit the 110mph
zone it's time to add a rear spoiler to reduce the lift created by this
airspeed. Even the old Herrod Helpers will help a good bit over 100mph,
or you can go crazy with a full on drag wing if you are really moving
(130+). Our Street Wing is for in between these 2 terminal speeds, and
it does keep the car straight and rubber side down.
We really hope this article helps you in setting up your car to be safe
at the track -- but don't be afraid to apply the principles and mods
to driving on the street. We have seen some street cars that were death
traps at 55mph, well under the speed limits in many areas. You can apply
these principles to make your street car the safest VW in the neighborhood.
Good luck, and let us know
if this information helped you setup your car!
LhYnxz- Site Administrator
- Number of posts : 485
Age : 44
Location : Bayamon, PR
Reputation : 0
Points : 30
Registration date : 2007-12-01 -
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