Adjustable Sway Bar Setup, Corner Balancing,Alignment Advice

[Theo]

Victor,

I often wonder about the 'push' or 'understeer' that people report with their air cooled VW's. I have always seen 'oversteer'. I wonder what type of setup would cause this? I was able to get my Ghia to push by using very low air presure front and rear but this was me tunning the car to the edge.

Many years ago we had an old splitwindow bus that handled really bad. It pushed and was very unstable. The problem was found to be front tires that were a smaller diameter than the rear tires. With properly sized front tires the bus handled great.

I do see a lot of bugs with small diameter front tires. Perhaps this is part of the reason why so many people report that air cooled VW's push.

2 cents

theo

rsnate- How do you have your car set up? Most beetles if properly set up will almost never understeer except at very low speeds, or with really high steering inputs at higher speeds (something most experienced drivers avoid). Weight is the enemy of corners and beetle front ends are light and rarely understeer unless something's not right. The rear end is another story. Two problems weight and high polar moment of inertia with the engine hanging behind the rear axle. Ever enter a corner too fast? You don't plow off in heavy understeer, your rear end will swing around like a pendulum and spin you off in a huge oversteer condition. Of course there are exceptions to everything but I think you'll find most beetle and early Porsche drivers wanting more rear end bite, rather than worrying about front-end grip.

[Marc]

Put too much front swaybar on and go fast, you'll get push.

[Victor H]

Yes, absolutely you can get a beetle to understeer if you have too small front tires relative to rears or if you have a big front bar and nothing in back. However, this is the Road racing forum and I am assuming that we are talking about optimizing the bug for track use and not talking about lowered bugs riding on the bump stops of their shocks while running 145/15 tires.
I run 195/60/15 tires all around so I can rotate them after track events. For optimal performance you would want a wider rear tire about 10-20 mm wider.
You can play with tire pressure, usually we run the max of recommended tire pressure (tire sidewall) and sometimes a bit more.

[Bill K.]

Corner weights -- are the weld-on adjusters from ACNthe way to go to get it dialed in easily? How's the install?

[Marc]

Installing rear torsion adjusters with the body on is a PITA if you ask me, and they're far from convenient to tweak. If you don't mind slotting the bodywork to put a weight jack on the outer end of the torsion bar, that'd be the way to go (you can't buy `em, but they aren't all that had to fabricate - adjustable springplates accomplish the same thing with a slight unsprung-weight penalty and they're an off-the-shelf item).
You can't move mass with spring preload adjustments so unless there's an inherent imbalance in your springing there isn't much point in fooling with corner weights unless it's to optimize the handling for turns in one direction or the other - you might find that just playing with swaybar preload will do as much for no money and no added weight.

[rsrnate]

victor my car is a track only setup that i drive on the street I run kumho 710 slicks in the rear and victoracers in the front. I am also a driving instructor for the porsche owners group so i might know how to drive I was just trying to be helpfull but take it as you will.

[Victor H]

Sorry, no downer intended. Just my experience is that understeer is not really that much of a problem in the beetle.

[gerico]

rsrnate,

on the street icon_biggrin.gif I run kumho 710 slicks in the rear and victoracers in the front

Sounds like a fine street setup to me.

[Marc]

... this is the Road racing forum and I am assuming that we are talking about optimizing the bug for track use and not talking about lowered bugs riding on the bump stops of their shocks while running 145/15 tires...

Nor am I. My experience is with ~10" wide slicks all around, with full front suspension travel (tube-chassis car, entire beam mounted higher-than-stock).

I would not put toe out in the rear as that would almost certainly make you spin off the track...

I did say "if you want the tail to snap out on throttle-off to rotate the car (and you can handle that) ...some of us can, even if we aren't driving instructors for dentists and lawyers.

[Bill K.]

Installing rear torsion adjusters with the body on is a PITA if you ask me, and they're far from convenient to tweak.

I found a picture of the Sway-A-Way unit -- probably the same as the one on ACN I mentioned above. I see what you mean -- should have considered that with body off.

I found your June 1, 2004 post on this subject in the Drag Race Forum:

You can adjust the L&R sides independently but it's a P.I.T.A. to have to get the car up that far safely for access to the adjusters, then drop it to check the results/repeat as req'd.
We used to make adjustable end caps for the outer ends of the bars, which added some weight (maybe as much as adjustable plates, but slightly further forward). Our rules allowed slotting the inner fenderwells so the "weight jacks" could protrude through into the cab, it only took a few moments with a ½" ratchet and extension through the rear ¼ window to crank up or down, then a couple more to tighten down the lock-bolts once the desired height is set - usually possible without even removing the tire. If this'd be legal for you I can send you sketches of what I'm talking about. Uses ~3/8" steel plate and a big (3/4" or so) bolt & nut, requires quite a bit of cutting & welding to fabricate but the design is pretty simple.

If you still have stetches you could send, I'd appreciate it. Thanks for the advice.

...You can't move mass with spring preload adjustments so unless there's an inherent imbalance in your springing there isn't much point in fooling with corner weights unless it's to optimize the handling for turns in one direction or the other...

Right, I'm talking about "cross weight percentage" not "static weight distribution" (this helped). I want to balance the diagonal weights with me in the car to get equal left/right cornering performance by adjusting the left/right rear ride heights. It seems like balancing the cross weights could make a significant difference in a bug considering that the drivers weight is relatively high compared to the corner weights. What's your experience with the impact of cross weight balancing on cornering speeds? Also, when the car is cross weight balanced with a 180 lb driver, is the car noticably leaning to the right with the driver in it?

...you might find that just playing with swaybar preload will do as much for no money and no added weight.

Good idea. As I understand it, the Whiteline adjustable sway bars can be set up asymetrically. A quote from post #56 (page 3) of this Subaru threadon the topic (heavy stuff...):

Taking this in total, what the data reveal to me is that asymmetric settings result in asymmetric response with the average side to side difference being about the same as a bar set to one pure setting versus the other pure setting. Or said another way, a bar on Soft/Medium will behave like a Soft bar from one side but a Medium bar from the other as opposed to a bar with a response that is the same on both sides but of an average value between the Soft and Medium settings.

So, I could setup the left side to be stiffer than the right to resist body roll due to my weight on the left. That's probably a simpler starting method, but is it equivalent to the results of cross weight balancing?

[Marc]

What's your experience with the impact of cross weight balancing on cornering speeds? Also, when the car is cross weight balanced with a 180 lb driver, is the car noticably leaning to the right with the driver in it?

Once the basic spring and shock rates are dialed in, you use tire pressure, cross-weight, and swaybar adjustments to produce the desired cornering behavior. Changing cross-weight also changes your swaybar preload, so the swaybars should be disconnected while doing it and then hooked back up "neutral" - you need to be able to access the links with the vehicle on the ground to do that (put equal blocks under each tire if needed to get yourself underneath).
Most cars need to run extra crossweight ("wedge") to help them transfer power to the ground more evenly when accelerating - a VW or Porsche has the opposite chassis reaction, accelerating adds weight to the LR tire, so you may find that less than 50% works better for you.
Let's say you want more crossweight - you're either going to raise the ride height on the LR and/or RF or lower it on the RR and/or LF. If it helps, think of it as a 4-legged barstool - if you trim a little off of two diagonally opposite legs, it'll rock on the other two, they carry the weight...on a car, the springs on the "long" corners will compress more than those on the "short" corners, making their tires carry more of the weight of the car.
If you were going the same way on both the front and rear on one side the car would develop a list, but small diagonal adjustments aren't going to have that effect.

[Bill K.]

...a VW or Porsche has the opposite chassis reaction, accelerating adds weight to the LR tire...

wow - that sets up a bigger weight imbalance -- driver and motor weighs down the left side. So does driver weight load the LF more than the LR so that a level ride typically needs the LR raised to get more cross weight? Thanks for covering this in detail!

[Marc]

But that's only on acceleration - it's the reverse on decel which means what's best for getting out of a turn may be a disaster going in. Compromises must be made; you can only take this so far on paper. What's ideal in theory is a good starting point but it's not likely to be the fastest way around, you need to run it.

[Bill K.]

Got it. Enough talk. Time to setup, drive and adjust. Thanks again.

[Bill K.]

Here's an update after putting on the SAW adjustable spring plates and getting cross-weight balanced with full tank and 200 lb of driver.

..............LF/RF
Wgt, lb 435/413
Wgt, % 20.2/19.2
Hgt 3"/3-1/16"

...............LR/RR
Wgt, lb 681/623
Wgt, % 31.6/29.0
Hgt 5-1/2"/5-3/4"

Total Wgt, lb 2152

Cross-weights:
LF-RR Wgt, % 49.2
LR-RF Wgt, % 50.8 (aka wedge)

Side-weights:
Left Wgt, % 51.8
Right Wgt, % 48.2

Rear-weights:
Front Wgt, % 39.4
Rear Wgt, % 60.6

The rear is set at 1 deg toe-in and -2 deg camber.

The front is messed up on the left. Can only get 0 to positive camber. New brazilian beam with bent C-arms? Anything I should check?

Right is maxed out with extra eccentric adjusters at -1.2 deg camber.

Closer
Bill