Reading your tire wear - info thread

[TBone]

Synner, major applause to you.

I have been sitting on an article similar to this for a while but just haven't been feeling well enough to finish it. So I am just going to add what I have to yours if you don't mind.

So I had to go to Discount Tire today because the better half had a tire that kept losing air. I swear she runs over everything. Anyway, the good news is it was just a nail and the guys over there got it all patched up for free. While I was there and had some time on my hands I got to thinking about folks talking about tire pressure at the track and the different tires we all use. Since I buy a lot of tires from DT, I am one a first name basis with the guys over there. So I asked if they had any high performance tires in each brand lying around and they did so I got to take some pix. Now I can show you what to look for as opposed to saying air them up to X amount.

When you track your car you always want to check your tire pressure when the tires are hot and the best time to do this is when you come off the track. In addition to this you also want to check to see how they are wearing because this will determine how much pressure you want in your tires. To do this there are wear marks on the side of every high performance tire that you can use. Ideally you just want your scuff marks to reach the tip of these marks. Here are some examples,









Now if you are over these marks your tire pressure is too low and if the scuff marks are not reaching them at all then they are too high. You want them to just reach the tips of these marks. On the Michelins, which I run, this is right around 36 PSI but can waver +/- a pound or two depending on weather.

Now, is this the best way to check you have the right pressure? Nope, it is the poor man’s way to do it but it does work. The best way is with a tire pyrometer with a probe that can actually get the tire’s temperature when you immediately come off track. A good one can run hundreds of dollars though and that equals one track day so, well, yea. If you have the money and want to learn how to do that then here is a website that has a good article about it. http://www.turnfast.com/tech_handling/handling_pressure

For the rest of us we can use a dial PSI gauge and the built in tire markers.

T.

GO HAWKS!!!

[Mikamaro]

Thanks for this info Tbone.

[SPCBA]

Originally Posted by cornerspeed92

Camber is stock/factory, PSI 31 cold

Was another thread where someone asked about these tires. As I said in there that is to much pressure.

[Norm Peterson]

Originally Posted by cornerspeed92

Camber is stock/factory, PSI 31 cold

Is that a verified factory preferred number (IIRC, -1.0° is the FE5 front spec)? Or are you assuming that's what it is because nobody has touched it since you bought it?

Really, it's worth measuring, because the factory allows some tolerance either side of preferred without bothering to correct it, and every once in a while a rogue car slips off the assembly line and out the door with cambers completely outside the factory range.


Norm

[EarlyApex]

Tbone,

An old school method to check that was to use the wax pencils tire stores have and color in a band across the tire. Where the color is wore away will equal the tire patch width.

[cornerspeed92]

Originally Posted by SPCBA

Was another thread where someone asked about these tires. As I said in there that is to much pressure.

This is something i will definitely be watching a little closer, as i just bought new tires for Miller in Aug. I thought setting at 31-32 was good, but apparently that's too much.

Originally Posted by Norm Peterson

Is that a verified factory preferred number (IIRC, -1.0° is the FE5 front spec)? Or are you assuming that's what it is because nobody has touched it since you bought it?


Really, it's worth measuring, because the factory allows some tolerance either side of preferred without bothering to correct it, and every once in a while a rogue car slips off the assembly line and out the door with cambers completely outside the factory range.


Norm

Exactly, im just assuming. How do i go about checking, or do i have to take her to the dealer?

[Synner]

Take her to a reputable alignment shop that will do a real alignment matched side to side. The +/- .5 degree window of "acceptable" per manual spcecs is a crock for high performance driving.

As I had said, check hot psi, cold is only where you set it based upon temp rise. Hot psi is the only number that matters as thats what impacts performance and tire life. The temp will continue to increase after each session so you need to keep going below your target psi to wind up there again during the next session.

[Dropspeed]

Originally Posted by Synner

Thats why I did camber plates but every company making them went tits up. Must be the camber plate curse. I go from -1.2 to -3.25ish by jacking up one side and loosening/tightening 4 bolts per side.

I was under the impression that when the camber is adjusted the toe needs to be adjusted as well. OR are you just setting the street toe and letting it self adjust to toe out at the track?

https://www.facebook.com/media/set/?...0443813&type=3


-Matt

[Synner]

Yeah they're both correlated; as you adjust one it dorks up the other. The pedders method is what I'm doing.

[cornerspeed92]

Originally Posted by Synner

Take her to a reputable alignment shop that will do a real alignment matched side to side. The +/- .5 degree window of "acceptable" per manual spcecs is a crock for high performance driving.

As I had said, check hot psi, cold is only where you set it based upon temp rise. Hot psi is the only number that matters as thats what impacts performance and tire life. The temp will continue to increase after each session so you need to keep going below your target psi to wind up there again during the next session.

So hot, what do i want to see?

[Synner]

35-36 has worked well for me but pressures can be tuned like everything else depending on conditions, sidewall stiffness, etc

[Norm Peterson]

Originally Posted by cornerspeed92

Exactly, im just assuming [edit - camber]. How do i go about checking, or do i have to take her to the dealer?

You can DIY this. Find a known level area to set the car on and just measure how far off plumb (vertical) the plane of the wheels' outer flanges are. A digital angle finder will get you within about half of its ±0.1° resolution, which is entirely good enough for most purposes. If the wheel spokes get in the way, you may have to make some sort of stand-offs. This gauge has a length of metal angle bolted to it to better reach wheel diameters, but longer gauges are now available. At a somewhat higher price point, caster-camber gauges are available from the various circle track supply houses, though I doubt their resolution is really any better.




But there are other ways if you feel like fabricating, or if you've only got a combination square and a little scale and don't mind doing the trig calcs. Sorry about the background, but I'm pulling pictures I used elsewhere for the same purpose of illustration.

Originally Posted by Dropspeed

I was under the impression that when the camber is adjusted the toe needs to be adjusted as well. OR are you just setting the street toe and letting it self adjust to toe out at the track?

You'll have to at least check toe after adjusting camber. Depending on where you adjusted camber, and on what chassis, toe may not change enough to bother, and as you note setting camber more negative will move the toe toward "out". In front-steer cars, that is. In a FWD car with rear steer, more negative camber gives more toe in.

Parallel strings stretched over pairs of jackstands, measure between the strings and the wheel flanges, calculate the individual toe angles.


And once you know how to make the measurements, isn't the rest just wrench work? Even caster can be determined on a DIY basis . . .


Norm

[Norm Peterson]

Not on a Camaro, but at least it's got a strut front suspension. I think it's a combination of not enough tire (255/45), a little too much pressure (37 hot), and not quite enough camber (-1.8°). Fully four of the five ribs are getting beat up on in the turns.

Wheels are 9.5" wide (max recommended), which I think is keeping the center tread wear from being as bad as the inflation pressure suggests (37 hot is close to what I run them at on the street, and there's probably 20,000 street miles on them). I'm wondering if the wheel width is affecting how far around the shoulder the scuffing should extend.

It was on the driver side front at the last track day, running clockwise. Set a personal best whole seconds better than previously.


Norm

[Synergy SATX]

Originally Posted by Synner

Spend $4500 and get a "free" camber plate. LOL. Their track setup is $6185. I'm too poor for that.

Concur. I knew they had them but not at that price.