So I did my first "real" as in actual SCCA full 50 second course type autocross yesterday. I've done a few smaller local ones in the past but this was the first big one. As an aside I placed 3rd out of 11 in BSP and I only have springs/wheels/tires/rear sway so I was pleased, no power mods yet.

On to the question: through most of the slaloms I would get a little chirpage but not a full on screaming of the tires, I think that's normal and proper. On one sweeping 180 I got full on screaming of the tires but I was able to essentially drift the circle and accelerate out the other side without issue. On the other slightly tighter 180, I kept having a weird almost grinding, wheel hop noise, definitely coming from the front but not sure if it was inside or outside wheel. Not full on tires screaming like I would expect but rather almost like I was bouncing. It didn't feel bouncy inside the car. I definitely didn't have much traction during this, but it didn't feel like a drift, it was almost like wheel hop in a drag car except I was moving laterally. What is this and what might I do to correct?

For reference, I am running 255/40/18 Michelin Pilot SuperSports on 18x9.5+25 Advan RZ-DFs. I have GTWorx Tarmac springs and a Whiteline rear sway bar on the middle setting.

Ideally I want to get Hoosier A6's and a dedicated set of rims for next year's autocross season anyway, but I want to know what I was doing wrong and/or whether the issue was driver or equipment or some combination thereof.

 

did you chalk your tires? I would guess your rolling over the edge of your tires a bit. What pressure are they inflated to?

 

No I didn't chalk, but I'm betting you're right, after I read this I went and looked and the inside front (in this case driver's side) tire from that turn does have a bit of shoulder scuffage. The nubbins are still visible on the passenger side shoulders. (These tires have about 4k street miles and 1 autocross on them now).

I had them inflated to 40 front 41 rear before running. After the 7 runs in about an hour and 45 minutes, the fronts were at 44 and the rears at 42.

So the solution is to up the pressure a bit?

 

I wouldn't even consider stepping up to A6's (or Rcomps in general) until you're more experienced and have full coilovers with stiffer spring rates

as for "sliding", it's tough to say without video. I always assume it's the nut behind the wheel causing it first

 

to me it seems like you were lifting a tire, and get excess wheel spin on that tire. I also agree with Exyia...learn to drive more and understand what your car is doing before you step up to R-comps.

 

You were experiencing excessive understeer. This is when you exceed the tire's capability so much that it chatters. In some cases it will actually hear/feel it resonate.

Other than adjusting your driving style (gradual turn-in, brake sooner, etc), you can increase front camber or add a little toe out. You may also need to lower your front tire pressure a little (but not too much). For street tires, 38-40 psi is a good starting point but it is best to monitor you sidewall rollover with chalk.

 

Some good posts here:

To sum up

- chalk your tires
- lower your tire pressure some
- Understeer is "pushing" the front of the car, where your front tire(s) slide (out) more than the rear, causing the car to steer less (under steer) through a given turns radius. Oversteer is where the rear slides more causing the front end to rotate more for a given radius "over" steering the turn.
- Your "chatter" is the car losing and then regaining traction quickly. This can be caused by tire pressure issues or too much rebound in your front suspension (I suspect smarter suspension people than I will opine here). If you can, try softening up the front suspension a bit, or adding rebound to the rear.

Don't move to an R comp tire yet. do get more AC/ track time.