josh7owens

We never had issues with the 255s Z1stars rubbing the fenders. Swaybar setting is full stiff on a 1.25 solid bar. Which is 3-4/6 on the monster bar. This guy is talking about tracking though, which would require less bar, the 235 may be the better choice for him.


Whats the new tow vehicle? You tease!

andrewhake

Wow I can't even imagine how sloppy the car must be on turn in with 255s on 7" front wheels. Even 225 is pinched on a 7" wheel. With the amount of rollover you get with a 255 on the front you might actually get more contact patch with a 235 or even 225 with the tire at full load I would think. Forgive my autocross ignorance, but are you not allowed to run wider wheels in RTR? Also I would have thought people in autocross would run relatively high tire pressure since there isn't a chance to warm up the tires, but I guess getting the highest level of grip out weighs feel?

josh7owens

Nope, stock wheel sizes only. They don't roll as bad as you might think, the Z1 sidewalls are pretty stiff if you look at my picture above the tires apear to be rolled over about the same amount. People put 275 A6s on the 7" wheels all the time. Granted that sidewall is stiffer then the Z1.

CKit

Lower pressure heats up tires quicker than higher pressure due to more motion and flex.

With pinching street tires, the tires start rolled over so there isn't much additional rollover. The whole rounded tread moves together and you still get contact patch all the way to the side. You DO have to wear in the tires to camber... you get more contact patch after they break in well.

andrewhake

I see. It would be pretty interesting to do a back to back test with 225 f and 255 front back to back.

I was getting plenty of rollover on the 8.5" rear OEM wheels at Laguna, but I suppose the loads are quite a bit higher and springs are quite a bit softer in the front compared to the CR setup. I guess that brings some of the feel back.

andrewhake

Ahh that makes sense. Is there much of a chance to warm up at autocross events?

CKit

Yes and no. Local sites and runs can be very different than National-grade events.

Star Specs have been great because they come in after about 1/4-1/2 run in most ambient temps on medium grip courses.

On high grip courses on hot days, they can overheat by the end of a run.

The number of grip transitions and resultant deformations really heat up a carcass.

I took a set of our pull-off 275 A6s mounted on 4 rear AP2 sized wheels to COTA. I couldn't believe how well they wore compared to just autocrossing them....

CKit

The other thing about Laguna is the elevation and banking that is going to wear sidewalls more than on flat ground.

andrewhake

Makes perfect sense. Thanks for the great info as usual. With autocross the tires are almost constantly under load where most tracks give them more of a break with the longer straights. I guess they are always heating up or maintaining heat as the car accelerates but all the quick transferring back and fourth that is logical.

What sort of mileage/life do people get out of a set of tires uses purely for autocross?

CKit

People usually go by runs, events, seasons and some street tire autocrossers will put on some highway miles going to and from away events.

Also, the tires can still have tread but start to heat cycle out. They get harder and need more heat to work. They're still fine to use as a regular daily driven street tire at that point.

People can get an entire season of heavy use out of them as autocross tires and then use them as daily tires for another 5000-1000 miles. But YMMV. Depends on camber and vehicle settings.

Josh and the STR boys can probably answer the question better than I.