-nick

NER region a/x on Sunday. I'm getting my driving skills back up but am having some slight trouble with the car. Yes, C4 is going to understeer, but it was feeling extreme on Sunday. There were a few almost 90* or so turns in the course and I couldn't carry any speed and had to almost crawl through in order to make the gates. A better line could obviously help, but I was running a few seconds slower than the gang of 3.2's that I can keep up with when I'm in my best form. Also, the tires were feeling more and more slippery toward the end of the day even though I was keeping them at 32F/36R psi before starting each run.

Anyway, here is the car setup. Any tips/experience for me or the car is always appreciated to get me going around faster!

1991 C4 Cab (double whammy), corner balanced, semi-aggressive alignment, 225/255 Dunlop star specs on 17" heavy aftermarket wheels, wevo motor mounts, front strut brace, h&r and bilstein combo with ~2* rake, not sure where the ride height is set but I wouldn't want it any lower. Everything else is stock and the engine has very healthy leak-down numbers and fairly recent valve adjust/plugs/caps/rotors and brake fluid.

I'm thinking swaybars might not be a bad idea by the look of this pic (thanks for NER photog Richard Viard!)

Vandit

Bigger rear swaybar would probably help.

How old are those Star Specs? I ran those on my Toyota daily driver for about 17k mi and definitely noticed the grip fall off as the tire got older.

-nick

Pretty darn new. Bought them last July and have barely put on 1k miles. They're only on during ax season and stored in a dry and dark basement for the winter. At 17k I would expect the rubber to be completely gone!

The Stig

I don't know much about autocrossing but I'm curious as to why you're running staggered tire pressure. I was under the impression that running the same pressure all around for C4s was better for handling on road/track.

Is this a nuance of autocross?

Vandit

Autocross tire pressure is somewhat trial and error and personal preference.

My C2 on blown stock suspension and old PS2s is really sensitive to rear tire pressure. Anything above low 30 PSI and the rear becomes way too loose. As a result of having to run low 30s in the rear, I am eating up the sidewall tread, but I can't comfortably push the car if I run a higher pressure.

Makmov

Probably just a rear bar and full tank of gas.

You know what they say.

If you are looking for a few tenths fix the car. If you are looking for a few seconds fix the driver.

Braking too late in those coners? Fast in slow out slow in fast out.

A drastic change in slow speed cornering will take away from high speed cornering.

You just need to find the balance, and I don't know does the car feel balanced to you?

Makmov

Typically you run them square it is a good place to start.

-nick

I fooled around with pressures last year. A smaller delta and the car felt like it didn't want to turn at all. 32/36 felt the best and was giving me the best times. Seems to be a popular combo for 17". If anything it should give more bite in the front.

I'm sure the driver is the biggest problem- no question! But getting the car to feel right can make a big difference in approach. I do tend more toward fast in through an a/x, which isn't always the wrong way to go. I would expect the car to really rotate with all of that weight pressing down on the front wheels under heavy braking. There were moments of going in too hot at a static acceleration and practically being at full lock and whistling a tune before the front end caught any traction to make the turn. I would be much happier having to counter-steer because the rear wanted to pass me in that kind of situation. So at this point I think the answer is: RS rear swaybar.

Derek Pedersen

Try defeating your PDAS (stability control / locking diffs) by turning the engage **** for 10+ seconds until it beeps. I noticed less understeer with it off.

-nick

^ I forgot about this new trick. I'll see what happens!

newsboy

I've never felt my PDAS/Stability control come on during Autocrossing. I believe that tapping the brake pedal disengages it. Switching to a 21 MM rear sway bar helped with understeer.

Gus

I am not sure about the tire pressure - but you can check it by looking at the tire roll ( wear point ) on the side of the tires - or chalk the tire to find how far over the tire is rolling - I ran the same tire pressure with Hoosiers last year - but have drop the pressure lower and am getting better bite front and rear now - you should be looking for a stiffer front setting and a slightly softer rear. Do you have adjustable shocks?? 2 inch rake may be a little steep, was it balance like that ?? Agree with Makmov / FISO- SIFO - it's important to find the straight line and be smooth - Ref "the Stig" - have never had / run equal tire pressures on the 964 - just doesn't seem to work for me

boxsey911

Purely on the point about tyre pressures I think your front pressures are too low in comparison to the rears. I always run the same balance front to rear on my C2. 32 at both ends for most track conditions (but that's for R compound tyres). By increasing the front pressures or decreasing the rear pressures, you should be able to reduce the understeer (to a small extent).

-nick

Odd, I thought the story used to be to decrease tire to increase grip? I just searched and am now seeing the opposite. I'll add a couple psi to the front and see how it rotates the next time out.

Gus, should read 2 degree rake. Was set up by, possibly, the best shop here in town.

Gus

Tire pressure changes significantly based on the type of tire/ manufacturer. That is why understanding the roll over on the tire is so important - use the tire marker to get an idea of what you are working with.
RAKE - ?? that is the angle from front to rear - you are trying to push weight to the front with that set up - has it been corner balance or have you weighed the car by corners? So you know what you are working with?