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posted: April 15, 2006 written by: John Connolly
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| Drag Racing Suspension and Setup for Type 1 | ||||
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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: Steering
Wheel Diligently
replace worn out parts, and replace with top quality
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.
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 Front
Toe Bump
Steer 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! 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. 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! 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 @$$).Guys who run Auto-X or slalom
in swing axle VWs often run rear Toe-out so the back end of the car
swings around faster. And as Mark Herbert once remarked, " Slalom
guys use toe out for the rear suspension. If you want to go straight
I think it's in your best interest to not use slalom alignment".
:-) As the car gets faster and
faster, it's going to "launch" harder. We WANT it to Launch
hard, but the harder it launches, the more load it's putting on the
shocks and torsion bars. What you do not want to do is slam down onto
your rear snubbers; because if this happens, it will shock-load the
transmission, possibly breaking parts, and if it doesn't break the gearbox
it will compress the tires and then bounce up off of them, which then
unloads them on the rebound, and then the tires spin since they are
off the ground or have almost no weight on them. Ideally you want to
use the available rear suspension travel, but not "bottom out hard"
on the snubbers. If you want to "do it right" AND have deeper pockets ($$$), 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. Good luck, and let us know
if this information helped you setup your car! |
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