Saturday it is was 90+ degrees ambient running on concrete. I am running Sumitomos, 235/40 on the front (stock size for the 04 GT3).

The car tends to understeer pretty badly, in my opinion, so I dropped the front tire pressure from the factory 32 psi to 29 psi. I think it improved understeer, but...

On the last turn of the track, which is pretty sharp, the front wheels actually start skipping near the apex of the turn, rather than simply slipping and squealing like I expect I get a juddering.

I never had this happen before in my limited number of autocrosses, so I don't know if this is a tire issue, a pressure issue, suspension issue, track surface issue, or no issue at all.

The suspension is a brand new Ohlins R&T with the dampers set at the manufacture's 10 clicks counterclockwise from full hard.

 

Skipping meaning a fast shudder like pushing a desk across the ground and it not quite sliding smoothly, or skipping meaning a slow hop?

A fast shudder is understeer, usually waaaay too much slip angle (aka far too much steering wheel angle vs. actual vehicle line.)

A slow hop where the car is bouncing off the ground like a basketball is likely a car / setup issue.

 

Thanks for the reply. This is a very fast (maybe 10 or so Hz) "shudder". I can just hear it on my GoPro's audio.

Actually, it's a stuttering screech. First is a brief screeching at the entry to apex, then it transitions to the vibrating screech and it is also evident in the steering wheel.

Post Script: Your 993 looks exactly like my old 993. Same awesome color.

So, it sounds like the slip angle is too much.

That begs another question: I assume that I am not setting up the turn correctly or not balancing the car properly (that is, braking into the turn and transitioning to the gas) and end up applying too much steering input to try to compensate.

If I can figure out how to edit out all the extraneous parts of the video I can post it here. This is my 7th autocross and I am not executing my turns well (as seen by my times). I am guessing my footwork sucks. I also find myself tapping the brakes in places I probably don't need too, but that's just a lack of trust in my car, I think.

 

Sounds like the 'ol death push to me, but could be wrong. Just entering too hot, and adding too much wheel past where the tires can provide grip. You'll get a feel for peak grip and learn to nibble around it with a few more events.

Not easy to balance a 911. In a normal car, the fronts do braking and steering, the rears put down power. The big breakthough for me in the learning process of 911 dynamics was realizing that the rear tires do 80% of the work, and the front tires just phone in suggestions. I started thinking of the front tires as rudders on a ship. They don't act very well to directly do the turning, they instead get the rest of the ship to do the turning.

Don't get me wrong, I'm still no master of the RR format, but I ended up starting to work with the car instead of fighting it after I changed this perspective.

 

How is the wear from rolling over on the outside tread block? On 235/19 RE71rs I've had pretty good luck running down to 26 or 27 psi, but I really don't have a ton of front grip problems on mine. We're usually fighting the rear grip. Once you have the tire pressure dialed in, you can start playing with sway bar and damper settings. If you can adjust compression separately from tension, you could drop some front compression. You could also move one or both sides of your front sway bar softer by one hole and see how that changes things. The softer you make the front bar and damper, the less crisp and "sporty" the car is likely to feel in transition, but it should improve steady state grip. You probably should also make sure you have at least -2 to -2.5 degrees of front camber and zero toe if its primarily a street car.

 

Funny........at the last Solo2 I was at we had a turn around pin and one of the guys noticed I was doing a left entry.....then a right entry.....then a left.....

He asked how I was deciding which side to enter......I laughed and replied "I'm letting the car decide".......if it was understeering a little I'd enter on the left......if it was oversteering a little I'd enter on the right.

 

I definitely agree. Slow in, fast out. Give up a little more speed before turning in, allow that front end to bite, and then roll back into the throttle gently as you unwind the wheel towards the corner exit.

Let me guess, it was around 15 years ago? I think that's about when the SCCA dropped the "Solo2" name.

 

Old habits die hard!

 

Ain't that the truth!

 

The older I get, the "faster" I was.......this year will be 50 years since I ran my first autocross!

 

Hehe......I'm getting faster in my mind too! Congrats on the 50 years in motorsports.