robfox

Did my first Solo 1/track day with my S4. I had major problems with trail-braking oversteer.

Here are some relevant vitals:

Stock brakes/pads
Worn 205/50 17 G-Force R1s
MTM springs (1" lower) with stock shocks

I haven't been happy with the tires all year but for this season of auto-xing I was happy to get them off of a friend VERY cheap. Still, they could be wider, but I don't think they should fundamentally affect handling this way.

I had to do ALL of my braking in a straight line or the back end would come around QUICK. I play with tire pressures auto-xing but these were fine and the car was more understeering than neutral as long as the brakes weren't applied.

A VERY experienced club racer/instructor (who holds a track record in his class at Gingerman) got to drive my car for a few laps and agreed that he had to brake in a straight line and there was definite oversteer induced by braking...I guess that's trail-braking oversteer.

I know that I need track experience more than anything but this really felt like something was wrong with car setup. I know most R compound tires today are not made for large slip angles, so I don't want to be hanging the back end WIDE early in the corner. I'd personally like my car to be understeering under braking coming into a corner and hopefully a little power oversteer coming out if necessary as I do at the autocrosses.

Anyway, your thoughts please?

Thank you very much (in advance)!

-Rob

Mike Zam

Too little weight in the back causing the ABS or traction control to go screwy?

Can you turn off you traction control? On our BMW's, we have to always turn ours off.

Could also be a brake bias that is not adjusted right?

And what are you doing with springs and not shocks and bars? You NEED to have a matching set to work properly together! Better get some KONI's soon, and some front/rear bars. Also, bleed the brakes and might as well add some ATE Super Blue, and maybe even the braided brake lines.

John/TSR

You're stock shocks aren't up to the job. Consider several things:

1. Shocks with some diddle, like rebound adjusters.
2. Forget trail braking for a while until you've got more experience. Whoever was coaching you to trail brake at your first track school should be shot.

Bollinger

Just so you know Mike. Hence, it is always turned off.

To be honest, they don't appear to need it.

Audiboy

turning, I figured the instructor doesn't see this. I don't mind as they set themselves up for an easy pass

Audiboy

In THILL, I had a lot of lift throttle oversteer, heck the car just oversteered quite a bit rounding the turn at even throttle, it was scary at times through turns 3 (carousel) but I knew it was because the tire pressures weren't set yet (cold presure 36F/36R) as I was still warming up the tires. When the tires where warm enough, got my gauge out, set them to 34 psi front/rear (I used 36/40 on the Kuhmos) and viola perfect balanced car (well, almost). Drifting was easy and predictable, mild understeer/oversteer depending on throttle and braking, and best thing, the super hard sidewall made up for lack of camber up front, very even scrubbing all the time. In AutoX, they didn't fair as well though, maybe I can't get them hot enough. The Kuhmo's felt better for that. Good Luck

John/TSR

Instructor should feel it, even if they can't see it. And they should see it too. I regularly watch students' feet on the pedals as they approach and enter a corner - just tilt your head and peer into the footwell. Most cars you can see the brake pedal, and some you can even see the gas. Several things an instructor needs to feel instinctively - brakes, clutch-up timing and tire loading. It's not just knowing the "line"....if an instructor can't feel what's going on as well as see what's going on, he should stay the hell out of the right hand seat.

Most of the time they're not intentionally trail braking, and will usually deny that they're doing it even when you tell them that you're watching their feet !

Brake in a straight line, dammit. We even insist race students start with straight line braking.

robfox

I don't get it. I do a skip barber school and learn the traction circle. I do a bunch of autocrosses in two cars and don't have problems. Now you say my instructor should be shot?

No one was coaching me to trail brake. I do mostly brake in a straight line...this track had some areas that just about required SOME braking while turning slightly. Second, if I got in a corner too hot, I had to straighten the wheel just to brake a bit.

Can you please explain to me what the shock rebound has to do with the problem? I think the MTM springs are only a little stiffer than stock.

I understand that braking uses tires, and cornering uses tires, and that you can't do both completely at the same time. But, why HUGE oversteer...you'd think a front heavy car with large front brakes would be breaking traction with the front tires first inducing understeer, wouldn't you?

Thanks,
Rob

Russ Burns

I drive my audi on a lot of dirt roads, and on dirt, the front/rear proportioning is rear biased. Trail braking is a lot of fun, almost like a handbrake turn. The brake proportioning in the S4 is now handled by the bosch 5.3 ABS unit. I am still trying to figure out how they did it technically. I also have noted at the braking exercises, the rear almosts always lock up as the S4 slows down.

As far as the track goes, I am still trying to sort that one out. I have found that with a light load of fuel, the rear end is very twitchy. Straight line braking may be very good advise on the S4.

Robfox, what speed were you taking the corners at?

Take care
Russ Burns

robfox

I don't know the exact cornering speeds, but I can tell you that on two straights I was going about 95 and would slow to 30-40 or so for many corners, maybe a couple even slower than that.

I think you hit on something...not only was I almost out of fuel, but I had the trunk completely gutted...F/R weight ratio must have been a joke. Also I could feel ABS kick on once or twice at as much as 40-50 mph, and many other times I think it was darn close. You think the rear wheels can actually be locking up because of so much front weight transfer?

Thanks,
Rob