Shark Racer

After 9 laps autocross laps in my C6Z06 on a heavily turn oriented autocross course with both drivers plowing a bit, we seemed to lose a lot of the car's capability to steer itself around the course.

Stock F1 SC EMTs, about 1 yr old with maybe 30% tread life left. A physical of the tires - they feel a lot harder than the barely 3 month old rears.

Is it time I invest in a spray bottle?

Mojave

Street tires can certainly over heat and lose grip. Falken Azenis are very well known to lose grip when they get too hot.

I'm not sure if a sprayer would help in your situation; it is definitely worth a try.

SouthernSon

In comparison to track compounds, the concept is really not explored that deeply by most. We just simply don't expect too much from the street compounds to begin with. The street tire will pump up from over heated air. I have seen 12 to 14 psi increase. Tread design is a great factor with street tire performance, also. Street tires like more psi to begin so one must be careful of pressures after each session. Just take it easier with the street compounds and don't expect to have your best times.

As far as heat, my last runs were on kumho 710's that had many heat cycles. It took 3 sessions to get the rubber sticky again. The last 2 sessions were nice with the rubber hot once again.

(I am talking roadcourse, 20 minute sessions)

90Z51

Street tires definately lose grip. I've autocrossed on street tires and gotten them so hot they had almost no grip at all.

95jersey

Sounds like an over inflation issue. While a tire will lost grip, I highly doubt 9 auto-x runs will do it. Many people tend to run street tires high in pressure and a few hot laps and the pressure goes up fast. I took a guys car for a ride one time and it handled horrible at the track and he couldn't understand. I checked his tire pressure and they were in the low 50's!!!!

I bleed them back down to 33 and the difference was very significant.

racerjon1

Yes x a billion.

Tires have operating temperatures, that range where they provide the best performance. Racing tires, depending on compounds can be anywhere from 150 - 250. (Hoosier autocross tire on the low end, Firestone IndyCar tires on the high end)

A street tire like the Falkens is somewhere in the 115-125 range.. In autocrossing we pretty much overheat those in a run, and always keep a spray bottle around to cool them down, the Bridgestone RE01Rs are now the "tire to have" for the street tire classes, and though I haven't overheated a set on an autocross course yet because of a lack of experience on them, I did feel them get greasy after 2-3 track laps on a road course.

Tire "grow" does play a roll as well, and to minimize the effects of overheating adjusting tire pressures each run is imperative. You have to balance tire "spring rate" on runs with cold tires vs a shrinking contact patch on later runs, I almost always find that I cannot "set and forget" tires when autocrossing.

Get a sprayer, hose them down. Especially with two drivers.

Jon K

davidfarmer

I totally agree, street tires are designed to operate "just above" room temperature, or in the low 100's as described. That is because that is how hot they get on the highway, where they are designed to use.

Race tires are good from around 160-220 F, again, because that is where they are designed to work.

I always used to laugh at folks doing smoky burnouts at the drag strip on street tires. Once you clean the "crud" off, any excess heat is only going to hurt grip.

naschmitz

I would agree that this is most likely overinflation. We run 1.7 mile autocross courses and halfway through the course on a hot day you can tell that the runflats have gained too much pressure. Once they get over 36psi front and 34psi rear the Goodyear runflats get really greasy.

I run with a RaceLogic PerformanceBox that measures G-forces during runs. I've never lost grip as the tires got hot even on the hottest days in August. Much more noticable is how much grip you lose on a cold day.

Z1NONLY

My brother and I ran his STI in STU (street tire calss) at the Subaru Challenge this year. We used a spray bottle (on his 615's)and the top two drivers in the class (co-driving the same car) were using one also (on re-01's). My guess is that a lot of the street tire guys were doing this. I noticed it on the co-driven cars most. (only about 5 min. between runs.)

I run kumho MX's and they seem to love the heat, but they started to loose just a little grip toward the end of our club's "fun day" yesterday. (about the 14th run I think) The course was about a mile long and fast. (3rd gear for my 350Z and 2nd gear rev limiter for the C-5 Z-06 vette that was there) It was only members and EVO school students so we had very little time between runs. I had to keep letting air out of my tires due to the heat raising my psi's, but I don't cool my MX's between runs generally.

Allthrottleandsomebottle

There is the issue.........I have tried to autox on EMTs that don't have much tread remaining like yours.........nothing is gonna help but new tires and non-emts at that!