Handling improvements for the 964 C4

[Bill Wagner]

I'd be interested in hearing about any and all handling modifications anyone out there has applied to their 964 C4s to help compensate for some of the understeer the AWD transaxle introduces.

FWIW: I accidentally type "oversteer" in the original post and have corrected it (thanks to Joe below).

In any case, anyone have suggestions???

Thanks

Bill Wagner

[stlrj]

Is it possible that what you call oversteer is actually understeer?

My understanding is that if the front of the car tends to go straight when in a turn, then I call that understeer.

If, on the other hand, the tail wants to swap ends, then that's oversteer.

Correct me if I'm wrong, but 964's have a tendancy to understeer, at least, the last one I drove did.

Joe

[Bill Wagner]

Yes, Joe, I meant understeer, not oversteer. In fact I'm going to edit the post. I do know the difference, I just made a careless error.

Thanks for pointing that out to me.

Bill Wagner

[stlrj]

What I did to eliminate all that annoying understeer was to reduce the front caster as much as possible and set the front wheels with about a half degree of positive camber which made an incredible difference especially in wet conditions, the front end now sticks to the road and feels much more contollable.

Joe

[Bill Wagner]

stlrj:

With this set up, how are the tires holding up. Also, when you say you reduced the front caster as much as possible, do you mean within acceptable factory limits, or as far as it can be adjusted. For example, my spec book says caster should be set at 4 deg, 25', with an allowable tolerance of +15' to -30'. Are you moving beyond these specs?

Anyone else out there try sway bar (front and/or rear) replacement/updates.

Thanks

Bill Wagner

[stlrj]

Bill,

My tires are holding up well, no unusual wear patterns with my set up.

As far as factory alignment specs, if you stay within specs, I would not expect any handling improvements other than business as usual.

Even going with heavier sway bars would not be within factory specs and would probably have a negative effect on your understeer problem.

So anything you do in order to change the way the factory designed the car to handle will fall outside of factory spec. and I have found that alignment changes are probably the most influential, cost effective way to deal with understeer.

Joe

[Bill Wagner]

Joe:

I think the theory regarding understeer and sway bars on the C4 goes something like this:

If you hit a corner fairly fast, the lesser sway bars (particularly on the rear), allow one of the real wheels to carry enough of an increase in weight distribution that the differential locks kick in (I know this for a fact, because my little "light" on the console flashes when this kicks in). This in turn causes the front wheels to sort of lock up in unison with the rear wheels via the center differential. This means that the front wheels are chugging along as if they are in a straight line rather than turning a corner. The effect is a "sense" of oversteer, but it's not the "natural" type of over steer you would see from suspension mods only, but rather "induced" oversteer. I hope I explained this properly.

In any case, the idea behind the addition of the heavier rear swaybar is to assist in reducing the diff locks from kicking in at times many of us would consider to be undesireable.

I'm really looking for confirmation of this theory. It makes sense, but it isn't mine.

Joe, my concern about "specs" was whether taking the alignment to what looks like an extreme would wear the tires out too quickly.

CHEERS,

Bill Wagner

[stlrj]

Bill:

I would seem that your concern over tire wear should be the least of your worries considering the fact that the lack of steering response at a critical moment on a mountain road or even a freeway off ramp could have potentially catastrophic consequences.

Regards,

Joe

[Bill Wagner]

Joe:

I'll look into your suggestion, but I'm leary of tire wear because a misaligned old car of mine chewed up a new tire in less than 1000 miles (it wasn't the C4 though).

Thanks,

Bill Wagner

[stlrj]

Bill,

Reducing the amount of caster on your car will not in any way cause your tires to wear out. But what has the greatest influence on reducing wear is too much toe in either direction and an alignment technician would never allow that to happen intentionally.

As far as radical alignment settings are concerned, it seems that Porsche took a giant step in that direction when they specify 4.44 degrees of caster on your C4. Typical AWD vehicles rarely go beyond 3.00 degrees caster.

The Audi Quattro runs 0.90 degrees caster, a Subaru 4WD runs 2.00 to 3.00 degrees depending on model. But I cannot find any 4WD from any manufacturer setting up their caster with more than that other than Porsche. And, as far as I know, Audi Quattro or Subaru 4WD cars do not have a problem with understeering.

Cheers,

Joe

[LPDandrea]

Bill,
I have a 91 C4 that I autocrossed this summer (7 events). For six events I struggled to learn to drive this car without massive understeer. Then I found on ebay a set of H&R springs mounted on C2 Turbo struts and shocks. These lowered the car some (1-1/2") and stiffened up the ride noticably. I put these in the night before our last autocross and I set the front camber positive as far as the adjustment slots would allow. I know that it sounds crazy to try this but I had nothing to lose. The rears cambered in just by lowering.

The next day at the autocross I couldn't believe the difference. Of course it still understeers under power, but turn-in and off/light throttle corner holding are amazing now. The guys that I normally battled each month (and usualy came up short) couldn't get within 1.5 seconds of me this time. For the winter I've had the alignment set back to factory but next sping Fordahl is getting my car to set it up right. I would expect some tire wear on the inner tread from these aggressive settings but for me it will be worth it.

BTW the C2 turbo and RSA share a part number that is different from C2/C4 but I haven't found anyone who can tell me the difference. Anyone out there know? They seem to work fine for me and they fit perfectly.

[stlrj]

Effects of Caster on Tire Wear
When set with a substantial amount of caster, the spindle travels in a vertical arc, causing it to move up and down and raise and lower the wheels as the steering wheel is turned. Because of this, camber changes occur. With a high amount of positive caster, the camber changes that occur, especially at low speeds in tight turns, cause the tires to show wear on their shoulders. In high speed cornering, the vehicle tends to continue straight ahead when the steering is initially turned. Due to this, and the amount of camber change that takes place when a spindle travels through its arc of travel, the shoulders of the tires on a vehicle may scrub and wear. When a left turn is made at a fairly high rate of speed with a vehicle which has positive caster, the caster of the left front wheel changes toward positive but the momentum of the vehicle is in a straight ahead direction. This causes the inside of the left front tire to scrub as it is turned. Just the opposite effect takes place on the right wheel as the vehicle is turned left at high speed. The right front wheel's camber will go negative but the outside edge of the tire is scrubbed because of the vehicle's momentum to go straight. On some vehicles setting caster more than +2.5° will cause scrub problems.

http://aligncraft.com/terms/terms.html#Front%20camber

To Reduce Understeer or Increase Oversteer

http://catalog.com/susq/other/stuning.htm