Stock tires on track - chunkalicious.

[SkiRideDrive]

So I ran my first track day in the frs yesterday. Ran streets of willow counterclockwise. Car is bone stock power and suspension wise. It does have upgraded brake pads and fluid. It was a bit warm, about 100. I was running stock tires. I set the pressures cold in my garage at 80 degrees - 38 front 35 rear.

This is the result: This is a picture of the outside of the right front tire. The rest show wear but no chunking like this.



I chalked the sidewalls and they weren't rolling excessively. I just don't think they were up to the heat. I was running mostly 1:37 and got down to 1:36 flat.

So it seems a set of tires and perhaps crash bolts is on the to do list. Any recommendations are appreciated.

I'd prefer longer wear and predictable release over grip. I enjoy sliding the car around and would rather it let go progressively rather than abruptly. If I can get away with mounting them on the stock wheels that would also be great as I am on a limited budget.

[CSG Mike]

you chunked the edge from not having enough camber.

Tires made for heat and abuse for tracking, generally also have more grip, and consequently, shorter life.

A second set of dedicated track tires is probably a better decision if you're going to be doing more than 1-2 more track days in the future.

[ZionsWrath]

You ran 38 cold? Didn't check pressure on track?

$50 pressure gauge and a few minutes could have saved them tires.

Also When you feel them losing grip from getting too hot back off for a lap.

If you want to get more serious you can get track tires and camber like mike said. But you still need to check tire pressures and adjust your driving in real time on the track based on what you are feeling. You can still ruin track tires with neglect.

[churchx]

Especially if it's easy to fit 4 full size spare wheels in trunk with rear seat folded

[EAGLE5]

Were you driving sideways perchance?

[DarkSunrise]

As Mike said you need more negative front camber and proper track tires.

Stock Primacy HP's are classed as "grand touring" tires, not really meant for track. Even on max performance Sumitomo HTR ZIII's, I was getting some light chunking. Once I switched to Nitto NT05's, the chunking went away entirely. Anything in the "extreme performance" category of tires should hold up decently at the track.

[mav1178]

Originally Posted by SkiRideDrive

So it seems a set of tires and perhaps crash bolts is on the to do list. Any recommendations are appreciated.

Also properly setting your tire pressure at the track after a session is a must. 38PSI "cold" at 80F will probably end up being like 42-44 PSI after a session.

Unlike autocross, your tire pressures need to be set for the conditions you will end up in.

-alex

[wparsons]

^^ I'd bet on higher 40's, but totally agree on the point.

[SkiRideDrive]

Thanks for the input. There seems to be a lot of "you need to check your tires at the track" responses. Some of them condescending. What pressures do you guys aim for at the track hot?

All of the advice for the stock tires I found were cold pressures. Also, my assumption was chunking was caused by overheating, which is caused by under-inflation. I aimed for 38 cold as that was on the high end of what had been recommended and would only grow with on track temperatures. Figured higher pressures would help with keeping temperatures in check and reduce wear, even if it caused a lack of grip.

I have run formula cars on track with three infrared tire temperature sensors per tire and suspension potentiometers along with 40 other data acquisition channels and tuned accordingly. Tires are not a foreign concept to me. I am not familiar with running street rubber on track however, I have always run slicks previously. The stock car doesn't really offer any adjustment of any kind so I just aimed for what I understood as the high end of the spectrum to prolong tire life and then tried to enjoy my day at the track. I am just looking for suggestions for a low cost tire that can withstand track abuse, don't necessarily need ultimate grip. Just using the FRS as a low cost tool to have a good time once in a while.

[SkiRideDrive]

If the higher pressures could have led to chunking, that would be great info to know. These tires are a bit harder to red than the slicks I am used to. Rather than graining in a particular way telling you if your too hot, too cold, too much spring, etc, the rubber just seems to rip out.

[Lynxis]

I'm running the stock Primacy's and I ran 31 cold, and saw it went up to 38 hot on track which seems to be a good pressure. My front tires look a lot like this now too but most of it came from autocross in my case. There isn't any reason you can't run these tires on track but I think CSG_Mike is right, you should get some negative camber in the front, even if you run a better tire.

[8R6]

well since you're probably going to replace the tires now anyway, get a pair of camber bolts (or crash bolts). itll probably help you dial in a bit more negative camber up front to about -1.5 or so. you can get even more negative camber dialed in with aftermarket suspension on most adjustable coilovers. that should help a lot with the chunking.

[mav1178]

Originally Posted by SkiRideDrive

All of the advice for the stock tires I found were cold pressures. Also, my assumption was chunking was caused by overheating, which is caused by under-inflation. I aimed for 38 cold as that was on the high end of what had been recommended and would only grow with on track temperatures. Figured higher pressures would help with keeping temperatures in check and reduce wear, even if it caused a lack of grip.

Overinflation reduces your already small contact patch, and coupled with the lack of camber would contribute to the excessive wear on the outside edges. Camber is your first fix, but you will benefit greatly from lowering tire pressure.

If I were you I'd aim for 35-38PSI hot and adjust down from there, based on your driving style.

On my car with aftermarket suspension + RS3s, I usually set it at 30PSI cold and end up with around 35PSI hot even at Buttonwillow in the middle of summer. I've put about 11 track days and 5k street miles on the car with this set of tires, and the tires still have about 1-2 more days left before they are to be retired.

-alex

[CSG Mike]

Originally Posted by SkiRideDrive

Thanks for the input. There seems to be a lot of "you need to check your tires at the track" responses. Some of them condescending. What pressures do you guys aim for at the track hot?

All of the advice for the stock tires I found were cold pressures. Also, my assumption was chunking was caused by overheating, which is caused by under-inflation. I aimed for 38 cold as that was on the high end of what had been recommended and would only grow with on track temperatures. Figured higher pressures would help with keeping temperatures in check and reduce wear, even if it caused a lack of grip.

I have run formula cars on track with three infrared tire temperature sensors per tire and suspension potentiometers along with 40 other data acquisition channels and tuned accordingly. Tires are not a foreign concept to me. I am not familiar with running street rubber on track however, I have always run slicks previously. The stock car doesn't really offer any adjustment of any kind so I just aimed for what I understood as the high end of the spectrum to prolong tire life and then tried to enjoy my day at the track. I am just looking for suggestions for a low cost tire that can withstand track abuse, don't necessarily need ultimate grip. Just using the FRS as a low cost tool to have a good time once in a while.

Cost effective?

Two camber/crash bolts, maximize that front camber, fix the front toe, and run some "extreme summer performance" tires somewhere in the 140-200 TW range.

The primary cause of your chunking is a lack of camber.

The theory behind a street car and your formula car is identical. Anything you learn here will carry over there, and vice versa. The difference is that you have to do everything yourself with this car, whereas with the formula car all the R&D has already been done for you.