Stock tires on track - chunkalicious.
 

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.

https://scontent-lax3-1.xx.fbcdn.net...91&oe=56945F16

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.

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.

You ran 38 cold? Didn't check pressure on track? :confused0068:

$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.

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

Were you driving sideways perchance?

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.

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

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

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.

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.

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.

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.

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

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.

Thanks for the input. Actually it was a Formula SAE project so we designed the car from the ground up and built it ourselves. My specialty was vehicle dynamics, designing the suspension system around the tire data we had available to us, choosing our dampers, springs, bars, and running the data acquisition/testing.

Lets transition what you learned in college over to the car, and you'll do quite well ;)

Am I weird for not considering formula sae as real formula cars?

Classify them however you like.

Wasn't an insult. Just never thought of them as formula cars.

I've interpreted formula as an open wheel car designed to a set of rules and assumed that FSAE fit within that envelope.

Alright, solving the camber issue.

From my research. I can take the bottom strut bolt and put it in the top hole, and put the SPC 81260 14mm camber bolt in the lower hole to achieve about 2 degrees of negative camber.

It also seems that each degree of negative camber seems to add about 1/16" of toe in per tire. Can anyone confirm?

Also, does anyone know the ratio of tie rod turns per 1/16" of toe?

This would speed up my alignment considerably.

Thanks!

Yes that the correct way to install crash bolts.
As for the toe setting. You really can't guess it with out having proper measuring tools.
Unless you have a toe setting plate and doing the the whole string and plumb deal, your best and fastest way is to take it to a shop. Sure it may cost a few dollars but it's a lot better than a DIY route. Unless you have alignment tools.

I was going to max out camber and then string it. For toe. Done it maybe 100 times before on an fsae car. Problem with a street car is you have to jack it up, put it down, jack it up, put it down. So I figured doing a little research beforehand would limit the number of iterations.

Not sure if you'll be back on stock tires, but I was most comfortable with about 35 psi front / 34 psi rear "hot" (as soon as I parked after I came off of the track) on a 100* day on stock tires. Set "cold" before my next session (about 2hrs between sessions) here in New Orleans, I was at about 31 in the rear, and 32 in the front. The following day I forgot to put air in the tires after leaving the track and my dummy lights were on for the tires (all <25psi) at about 75* in the morning. I felt like the rear starts to slide a little bit and the front understeers with 2psi more air than that. With 2psi too little air, the car feels more "squishy" like it doesn't want to settle when I was transitioning through "S" curves.


That could just be me though, I'm still pretty new to all of this track day business (only 4 days on the NOLA track). And this was on bone stock suspension/camber/tires.

Thanks for the input.

I actually found a deal on a few used stock tires so I am going to swap out the chunked tire for now in the canyons and work on a solution for track days. I also ordered the camber bolts and will install them soon.

Thanks for the input on tire pressures for stock tires. I've got my first track day coming up in the BRZ and I don't feel like buying real tires for one track day then leaving them sit all winter. :) That said, maybe chunking the stock tires will let me justify better rubber sooner :thumbup: