Tire Pressures

[Dissembler]

My car has been chewing the outside edge of my tires at the track, and I was wondering how best to even out the wear.

I dont remember the exact alignment specs, but I think its about -2 degrees camber front, -1.75 rear. Tires are 205/55/16 RA1s and I have the pressures set to 34psi front and rear as one of the the driving school instrutors told me about 6 psi higher than door sticker is a good place to start. The tires are filled with nitrogen, confirmed that pressure only went up 1 psi after several 15 min sessions.

Any advice? Thanks!

[xwill112x]

run 36 psi?

[nando]

more camber. -2 degrees is barely more than stock, try adding another degree. And if you have really soft suspension, rolling over significantly can throw your dynamic camber into neutral or even positive territory. This shouldn't be a huge issue with enough caster but it's worth thinking about.

get one of those $30 infrared pyrometers - not quite as good as the $200 ones that actually press into the tire, but you can get a much better feel for the correct pressures. hold it close to the tire to get an accurate reading on the middle, inside and outside edge. you want to get the temps as even as possible, with preference towards the inside edge being hotter over the outside edge.

also you need to recheck the pressures when the tire gets hot. eventually you'll have a good idea what you need to set it to cold to reach your optimum hot pressure. nitrogen is nice though, costco uses it but they won't fill tires that you didn't buy there anymore. :(

Anyone telling you that you need to run X-psi without having tested it themselves on your car with your suspension is just guessing.

[jlevie]

RA1 tires would like to see 3-3.5deg of camber and zero toe for the front wheels and 2-2.5deg of camber and 1/32-1/16" total toe in the rear. Cold pressures will range from 28-34psi (for air filling), depending on ambient temps, the length of the run sessions, and the track being run. Hot pressures should be in the high 30's to low 40's. But the important thing is to adjust pressures so that the tire temperature is 200F. Since tires cool quickly a check a hot pit check should show temps just a bit under 200F. If you see 200F or more, the tires are probably running too hot. The temperature check will also tell quite a bit about the contact patch, as nando stated.

[Dissembler]

I should state that this is my DD and the only mods I have done are PBR ceramic brake pads and the bilstein lowering springs/sport shock combo.

Is it possible to "move" the hotspots of the tire around with pressure? If the pressure was low, the hotspots would be on the outside, while if it were high the hotspots might move more towards the middle?

If I want to save my tires, the only real solution would be to invest in camber plates and a thermometer, then adjust the camber at the track according to temp readings (although this is something I don't think i would be too good at at first)?

[nando]

You can to a point (if the center is too cold), but you really need to dial in the camber for those tires. you can just set it within the general reccomendations (-3 to -3.5) and see how your temps compare. then set it back to -2 for the street.

[Dissembler]

alright, i'll give it a try. My next time out on a track won't be till september, but I wanted to get some info early so I had time to prepare :) Thanks for the tips

[jlevie]

I should state that this is my DD and the only mods I have done are PBR ceramic brake pads and the bilstein lowering springs/sport shock combo.

Is it possible to "move" the hotspots of the tire around with pressure? If the pressure was low, the hotspots would be on the outside, while if it were high the hotspots might move more towards the middle?

If I want to save my tires, the only real solution would be to invest in camber plates and a thermometer, then adjust the camber at the track according to temp readings (although this is something I don't think i would be too good at at first)?

If you are going to run RA1's, or any other race tire, you will need more than minimal mods. At the least you need adjustable camber plates and should have rear camber/toe adjusters. You are also going to need stiffer sways to limit roll induced camber changes.

Or you could run a different tire. Toyo R888 tires are happy with 2-2.5deg front camber. I'm not sure about what Nitto NT-01 tires like.

For the possible cost of a six-pack, you can probably find someone at the track that has a pyrometer to take tire temps for you. To get meaningful results you have to bring the car into the pits towards the end of session without any cool down laps. And the temps need to be taken as soon as the car comes to a stop. That pretty much means having someone in the pits waiting for you with pyrometer in hand.

It you get the camber and toe in the range mentioned above, you'll be real close and will get decent life out of the RA1's. That is a bit much front camber on the front tires for the street and you will probably want to dial the camber back to 2deg or a bit less. You'll have to have a camber gage to do that or have it done at an alignment shop.

[nando]

in my case -2.0 to -2.5 degrees isn't quite enough for the R888s. it's close, but I think they'd still be happier at -3.

any idea on optimum temps on the R888s?

as far as changing the camber, I'd think making a couple good scribes on the plates, one for your street setting, and one for track, would make it simple without having to spend $100 on an alignment every track weekend.