Taking Care of Tires on Track - How to Avoid Chunking
 

Hi all,

I've been a member at the local track for ~3 months. Up until now I used OEM Michelins, which were really fun and predictable. Unfortunately, they had to endure my learning phase driving: overcooking corners, too hard/abrupt on the brakes, relying on understeer to slow down, early apexing and pinching turns... I also set the tire pressures at around 35psi and didn't mess with the setup until I corrected my own mistakes first.

Here is what my front OEM tires looked like after ~5 days at the track. I am assuming this was a combination of my rookie driving mistakes, Texas heat and having zero camber up front.

http://i66.tinypic.com/29c8d4o.jpg

I recently went out with one of the instructors, who mentioned that I have come quite a long way since I started, so I think it's time for me to also put some thought into car setup. I already got some camber bolts and maxed the front camber (~-1.3 degrees on SPC bolts). I also got some new tires (Firestone Firehawk Indy 500, they say it's identical to Bridgestone RE003 in Asia) and managed to test them out this weekend. I monitored my tire pressures not to mess my sexy new tires like the OEMs and here is what I got after a ~20min session, starting with 35 psi all around: front left 43, front right 41, rear left 39.5, rear right 38.5. CW track with 75F ambient temps.

New tires after the trackday:

http://i68.tinypic.com/1zdbu6r.jpg

So my questions to the experienced drivers out there:

- Are these high front tire pressures expected?
- Is there a specific pressure to shoot for? I usually hear 38 psi hot as a good baseline and doing pyrometer measurements etc to dial in
- Is there a driving technique that is less punishing on front tires? (I am already late apexing most corners on track and don't trail brake too aggressively)
- Any advice on how to avoid chunking tires on track? Spraying them between sessions to cool down?

I understand harder driving means quicker wear. I just want to avoid the chunking issue that I experienced on OEM tires and to have even wear.

- Your temps are what can be expected starting at 35psi which is too high. I suspect your track runs clockwise as well and your front left may need to start 1 psi lower than the rest.
- 38 psi hot is good for street tires.
- Start them at about 32 psi.
- You will need to adjust them down to 38 psi immediately after each and every session (in the pits without a long cool down lap). If a tire is one or two psi under pressure (usually the rear) wait until the next session before adding any air.
- Don't bother monitoring temps while only using camber bolts. You won't get enough camber to make a usable difference. You need -3.0 degrees minimum in the front to stop the shoulder wear no matter what driving technique you apply.
- I'm not sure what you mean by "already late apexing" but if your front tires are screaming, growling, rolling, pushing or doing anything you can hear or feel, then you're probably entering the corner too fast. This would indicate understeer and cause premature front tire wear.

If you're serious about getting "correct" pressures and camber you will need a pyro.

Try using chalk. I read about this in a race car setup book (I used to really be into sim racing so I read a lot of engineering and technical racing books)- draw a chalk like on the sidewall of the time from the tread to the middle of the sidewall. At the end of a run, check the chalk line. If the chalk is worn off onto the sidewall, your pressure is too low. If the chalk doesn't wear off on the entire tread area, your pressures are too high.

I do this when I autocross and it helps me dial in the right air pressure. I ended up around 29PSI, but remember in AutoX you do one run, not laps

We've had people who used 215 NT01's on standard wheels. Even with camber bolts at around 1.5 Degrees they still work the outside shoulders a fair bit. Depending on track setup to get even tyre temps (pyro) I usually run around 3.5-3.8 Front left and 3.2 Front right camber on a clockwise circuit. Seems somewhat normal for street tyres. They can't handle the temperatures and just shred. Hence why they are made to be around 50C and track tyres are made for 80-100C

I was told the top of the little tiny triangle is the point where the tire ends the grip. (or maximum wear, hard to explain) someone else may be able to explain it better. You can see in your picture there's a line going all the way around the tire, but that line doesn't touch the tip of the tiny triangle. Just given that, I would say it would be safe to say to lower the psi just a bit to see if you can get that lined up that way you are using the full tread of the tire for maximum grip.

Chalk and triangles aren't terribly useful IMO a pyrometer is better, and there's no magic tire pressure, every setup and drive is different.

Changing to a more track oriented tire and adding camber are the only solutions outside of absolutely babying the tires, which probably gets boring quick.

Totally agree with your second comment but the first comment is inaccurate. Tires have very specific pressures where they function the best. .5 psi one way or the other and you will have adverse handling. So there is a magic tire pressure for each given tire. BFG, for example, has a chart you can download. Maxxis RC1s are great at 38 psi (if I remember right). 38.5 or 39 and you're understeering. My Pirelli Slicks function at 28-28.5 psi hot. 29 psi and you'll understeer. 27 psi and you don't get all of the grip that should be there.

But the pyrometre gives a reading for tyre pressure. For your setup there will be a best tyre pressure and the only way you will ever find that exact pressure is via pyro.

Thanks for the very useful advice everyone.

I am planning to monitor temps closer and start by shooting for 38psi hot. I will also try the chalk trick to verify that I am not rolling tires onto shoulders.

I am still reading up on how to use pyro readings to adjust tire pressures, but those measurements seem more relevant to make camber adjustments, which I am currently maxed out at. Still need to understand what temp distribution tells about tire pressures other than hot center --> deflate, hot outer edges--> inflate.

I really don't want to go for extreme summer tires to preserve the playful character of the car, but might have to go that route if my current tires can't cope with the heat.

You're kinda saying the same thing... he said every setup and driver will be different.

What pressure works for your car will be different than mine unless we're running the same spring and damper rates, alignment, etc.

To really set pressures and camber you need a pyrometer, good lap timer, and consistent driving/weather. Just because a car starts to understeer more with 0.5psi higher pressure doesn't mean it's slower, it might be generating more grip and have higher cornering speeds, it just shifted the grip balance rearward a bit.

Hot shoulder -> too little camber
Cold shoulder -> too much camber

Speed Academy has a great video on setting tire pressures and camber using a pyrometer:

[ame="https://www.youtube.com/watch?v=onl7o_l78mw"]How to use a Tire Pyrometer - Just the Tip - YouTube[/ame]

In short, there is definitely a correlation with temperatures between tire pressures and camber settings.

Because you've already maxed out your available camber and I can already tell you that bolts alone aren't enough, you can expect the outer edge to be quite a bit hotter than the inner edge. What you are going to want to look for when setting pressures is to see your temperatures across the tire be about evenly spaced. I don't know what the real numbers will be but something like 110 inside, 120 middle, 130 outside is a good spread and indicates good pressure. If you've got something like 110 inside, 125 middle, 130 outside then you might be slightly overinflated. Alternatively, something like 110 inside, 115 middle and 130 outside might be slightly underinflated. The point is to aim for an even spread of temperatures from inside to outside. Note that depending on the camber and the tire, you may not be able to get the values completely evenly spaced so just shoot for as close as you can get.

Thanks a lot, that is awesome input. Those tires are completely different from what I have though:

http://www.tirerack.com/tires/tires....omCompare1=yes

vs

http://www.tirerack.com/tires/tires....omCompare1=yes

I bought these tires specifically because they have very large shoulder tread blocks (same as re003) which I am hoping will help with the chunking issue. It is also a cheap and high treadwear tire which keeps some of the playful and fun character of OEM tires.

Did you use 2 sets of camber bolts, or some other method to get 2.5 camber? Might as well go that route before I wear out the outer shoulders on the new tires.

(Edit: Nevermind, I saw that you were using camber plates in the video.)