Autocross tire pressure help

[Rmcnelly]

.......

 

[krs]

I have similar camber as your setup, 0° toe front and rear. I’m running 255/35/R18 and today my new RT660’s felt amazing at 38f 42r, which is what I kept that at through all my runs today.

 

[xXDavidCXx]

The stiffer the suspension, the faster you drive, the harder you brake, and the more lateral Gs you can create, the more tire pressure you need.

I suggest 35/35 cold, and then adjust for temps and conditions. Your 38/36 was probably pretty good.

The tire tread needs to be supported and on a heavy front bias FWD car, the front tires take a lot of abuse. Higher tire pressure is how we counteract all the demand on the front tire.

Don't listen to a guy who runs low tire pressure and complains of understeer.

 

[krs]

Minimum wheel width per Falken is 8.5”.

 

[krs]

Thanks folks! The driver of the Golf R had a lot of Autocross experience, but not in a front/AWD car (the owner of the Golf R wanted them to drive it and see what they could do).

here was their best run. I’ve learned a lot by looking at their throttle input.

I tried some real low tire psi, like near 32 in the front on RE71R’s and damn near scrubbed the lettering off the sidewall it rolled over so much.

I’ve learned psi’s are like someone’s favorite flavor of cereal. Everyone has their idea of what’s best, but you really have to take them all as a starting point and find what works for your setup, on your course, on that day.

I have different tire settings for different surfaces of all the different venues I hit, but I sure don’t have the experience that some people do.

 

[xXDavidCXx]

Also wondering if I can squeeze 255/35 RT660's onto these 18x8" ET45 wheels with the amount of camber I have (-3F, -2.3R). Tires in the photo are 235/40-18 RT660.

View attachment 253041

View attachment 253042

The 255 660 is a very wide tire, wider than the outgoing 265 RE71r, on a 9-inch wheel. I would not go any larger than 245, if it's available in the correct ratio.

 

[krs]

Lots of folks running wider tires than recommended wheels, I'm more concerned with tire clearance.

Ah yeah, what's the term? Pinched I think it was? Guess it's better than stretched for the stanced br0 look. But that's not what I read you were initially asking.

I fit 255/35 on a 18" ET45, on the minimum recommended wheel width and don't rub, and my camber is similar to yours at -3.0° F and -2.0° R with the ride height looking around the same.

 

[xXDavidCXx]

I’ve been trying lower pressure on my favorite on/off ramps and the car felt good at 31f/32.5r.

Maybe I was just over driving the car when I first got the RT660’s, and not having adjusted from the MX-5.

I’ll try starting at the recommended 30f/32r next Sunday, and will keep my tire pump in Grid in case I don’t like it

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.

 

[SouthFL_Mk7.5]

My son runs 40psi all around on his 660’s on the GTI at the local autocross.

 

[enobiko]

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?)

 

[SouthFL_Mk7.5]

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]

42 f / 42r here

 

[krs]

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.

 

[MonkeyMD]

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]

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.