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Autocross tire pressure help

SouthFL_Mk7.5

Drag Racing Champion
Location
South Florida
Car(s)
2019 GTI S
Is there a difference for those of us running stock wheels and high-performance street tires (Michelin PS 4S) versus those running 17" wheels and more track-focused tires (RE-71R's, etc)? That is, I wonder if the stiffer sidewalls on the track-day tires work better with lower tire pressures than the street tires? I've heard the RE-71R tires ride hard (and are noisy), the newer RT660s and A052s are not a whole lot better.
On a related note for dual-mode (street and autocross) setups, how far from the standard recommended toe-in settings can you go before you start seeing negative after-effects on the street? Do you lose straight-line tracking, or higher tire wear, or what? My last GTI was within factory specs, I have not had the alignment checked on my current car (the local autocross site got repaved and they have not allowed us back this year...yet?)

On the GTI, even with as little as -1 camber and 1/16 Toe, we once ran an Autocross event earlier this year on PZeros (not in the same category as your 660’s V730’s or RE-71R in terms of track/autocross specificity) on the stock 18” Austins at 39psi with no excessive wear. At -2 Camber up front I ran it a few times at Sebring and Homestead HPDE’s with even wear on the PZeros at 36psi (less sharp lateral transitions that autocross).

On the other hand, with close to zero negative camber up front, my Acura ILX using 225/45/17 Pirelli PZero tires, the factory camber setting, just after a couple Autocross events is really wearing the outer tread to sidewall area due to all the rollover- just a couple more events will probably create damage. I’ve tried to compensate for the lack of negative camber and lack of stiffness of sidewall by over-inflating to about 42psi…. but this brings about other problems like lack of grip and accelerated heat buildup. The solution to the problem is to add more negative camber and to run an Autocross specific tire.
Could I run a 660 on the stock alignment on my ILX and get through more events at a lower psi? Probably. The 660 just visually seems so much more of an aggressive tire at the outer shoulder structure compared to the PZero.
 

odessa.filez

Autocross Newbie
Location
Roswell, GA
Car(s)
2016 GSW 1.8tsi auto
42 f / 42r here
 
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krs

Autocross Champion
Location
Reno, NV
Car(s)
MKVIIS R
Is there a difference for those of us running stock wheels and high-performance street tires (Michelin PS 4S) versus those running 17" wheels and more track-focused tires (RE-71R's, etc)? That is, I wonder if the stiffer sidewalls on the track-day tires work better with lower tire pressures than the street tires? I've heard the RE-71R tires ride hard (and are noisy), the newer RT660s and A052s are not a whole lot better.
On a related note for dual-mode (street and autocross) setups, how far from the standard recommended toe-in settings can you go before you start seeing negative after-effects on the street? Do you lose straight-line tracking, or higher tire wear, or what? My last GTI was within factory specs, I have not had the alignment checked on my current car (the local autocross site got repaved and they have not allowed us back this year...yet?)

I’m running pretty close to 0° toe f/r and haven’t seen any negative wear on my daily tires in about 12k miles.
 

Rmcnelly

New member
Location
Portsmouth, VA
Car(s)
2017 Golf Alltrack S
I don't see 30/32 as the recommended pressure.

What surface do you autocross on?

Trust me when I say, this is not the way.

Asphalt. And I believe you!

I tried it this weekend and so much oversteer and sliding! The car settled down as I increased pressure at both ends and only had the rear 1psi higher than the front.

I have a practice Autocross on Saturday and will have time to experiment.
 

Rmcnelly

New member
Location
Portsmouth, VA
Car(s)
2017 Golf Alltrack S
Sunday's best run, probably at 32f/33r and still sliding at the crossover. I completely blew the last couple of sections, costing me about a 1/2 second. Was pretty hot and I'm old, and lose concentration in the heat. Still, was a fun course, and working on getting better.

 

Rmcnelly

New member
Location
Portsmouth, VA
Car(s)
2017 Golf Alltrack S
That event also resulted in this on the right front tire. The tires didn't show signs of rubbing in two prior events. Both left and right fender screws were polished, so I did the fender screw mod today.

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610785E9-5063-4FE6-A2F8-EEC2A1C1DDD5.jpeg
 

MonkeyMD

Autocross Champion
I noticed on concrete i needed more pressure. So instead of 33F, ran 35F and 40R.

On asphalt, 33F is fine for my car and my suspension setup. There are so many variables to this though.

F 2.4 camber, 0 toe
R 1.6 camber, 0 toe
RE71R 255/40R17
 

xXDavidCXx

Autocross Champion
Location
AZ
Car(s)
2017 GTI SE DSG
I noticed on concrete i needed more pressure. So instead of 33F, ran 35F and 40R.

On asphalt, 33F is fine for my car and my suspension setup. There are so many variables to this though.

F 2.4 camber, 0 toe
R 1.6 camber, 0 toe
RE71R 255/40R17
The more grip the more tire pressure, in general.
 
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