Inside Tire Wear on Autocross Tires?

Anyone know the cause of inside tire wear on AX-only tires (ZII)?

I'm pretty sure it's not too much toe out, because it's the alignment was set to no toe out and my DD-only (RE-11) tires aren't showing inside edge wear.

Is too much camber possible? I have camber set to -1.8 now which seems really conservative. The car is a Fiat Abarth and it is set at -1.5 from the factory. Caster is at factory spec 2.65 and toe is at factory 0.

Another possibility is that the courses I'm running on are mostly straight or I'm not turning hard enough.

In terms of tire pressures, I've measured the tire temps and what I've seen is a temperature gradient across the tires. It's hottest on the inside edge and gradually cooler when moving to the outside edge. Maybe I should pump up the tire pressures so the middle gets some wear too?

I usually set the pressures to 45 cold in the front and 35 cold in the rear.

Inside wheelspin?

negative camber will wear the inside more as im sure you know, when turning there is a lot of friction on the inner side of the tire due to wieght transfer, is it excessive wear or?

-1.8 shouldn't cause any excessive inner tire edge wear (at least that's my free opinion )

I would, just for shoots and giggles, check the toe to make sure nothing has changed (yeah I know you said your DD tires aren't showing any wear) … if you are changing your camber at the a-x's … keep in mind that camber changes can (usually do) cause changes in toe … so if your changing at the site and then changing back for DD … that could be the culprit

I would doubt that it is camber. In all of my FWD cars, anything less than about -2.5 actually improves front tire wear.

Are you sure the alignment is still correct? What are the actual tire temp numbers? Both tires wearing the same?

I know some (even some on here) swear that excessive camber (which would be much more than you've got) will cause inside tire wear … but I run 3 1/2° neg. camber on the front and have never experienced any inside tire wear …

but excessive toe on the other hand (toe in OR toe out) will kill a tire in a hurry

nilfinite wrote: In terms of tire pressures, I've measured the tire temps and what I've seen is a temperature gradient across the tires. It's hottest on the inside edge and gradually cooler when moving to the outside edge. Maybe I should pump up the tire pressures so the middle gets some wear too? I usually set the pressures to 45 cold in the front and 35 cold in the rear.

Step One: Get the toe in/out checked again.
Step Two: If toe is OK, LOWER tire pressures and check temps again. You should be seeing the temp change in the opposite direction (outside hottest).

what he said … with no more camber than you have, I'd still bet on outside edges getting hotter than inside edges

Do you have inside wheel spin? If not, is your car lowered a lot? I ask because if you have camber loss under compression, you will have camber gain on extension. Switching to race rubber will cause more body roll, which will increase your camber on the inside wheel whenever you accellerate. If you are exiting corners with 8 degrees of camber and spinning, that would kill the inside in a hurry.

My ZX2SR showed slightly cooler inside temps even with 2.5 negative. 0 toe. Wear was good.

I go along with what DoD said.

I'll have to look out for inside wheel spin the next time I autocross.

The left and right front tires are wearing the in the same pattern, most wear on the inside edge. There is some wear on the outside shoulder from rolling over.

Rear tires show even wear. Outside edge of the rear tires being a 1 or 2 degrees hotter.

I'm lowered on Bilstein coilovers, about halfway in the height adjustment range.

It's about 1/32" on the inside treads and 4/32" on the outside treads of the ZIIs. When measuring temps, the inside edge will be somewhere around 120 and the outside edge will be somewhere around 110.

The body roll + inside wheel spin idea could be it. The Bilsteins don't have particularly stiff springs 285lb/in on the front and 217lb/in on the back. The amount of caster on the Abarth is also really low.

The uneven wear has also become a lot more obvious recently. Most of the runs on these tires were at an Evolution School and after. I want to say before the school, I didn't notice very uneven wear.

I used to also run higher tire pressures around 50 or so cold. When I ran those pressures, noticed the middle was the hottest, the inside side was generally hotter than the outside.

Its probably spinning a little bit pulling out of corners since its an abarth.

Most likely toe. I run -3.5 in front and -2.5 in the rear camber (different vehicle albeit) and I get very even wear on track only tires. Toe out will shred tires very fast though.

+1 for toe out, always a far bigger culprit for inside tire wear, especially in combination with camber. Camber itself is fine when suited to how the car is driven.

-3* camber all the time up front. 0 toe. Front tires are worn to beat all hell on the inner tread block after 9k miles of DD. The race tires never wore the inner edge because they were run much harder.

The inside wheel spin idea is sounding more like the culprit. Especially because the Abarth doesn't have a LSD and I have a bunch of mods in the car pushing it from 160hp stock to 200hp+.

Now, the next question is, how do I solve inside wheel spin without going for a LSD? I'm running in STC so I can't get a LSD.

Does a stiffer front roll-bar help? (I see suggestions on both extremes, stiff front roll bar vs disconnecting the front roll bar) Should I set the front height lower? Should the tires have a lower diameter?

I'm planning on getting caster correction bushings to up the caster a bit but it sounds like that won't solve the inside wear problem.

I'll try measuring toe the ghetto-man's method with the two tape measures. I'm fairly certain it's not toe just because the DD tires are wearing evenly and I drive a lot.

nilfinite,

You sound like you're too low and WAY too soft. I would strongly advise against a bigger front bar. I would raise the car to near stock height and double the spring rates. I would disconnect the front bar because the last thing you need is to transfer weight from the inside tire to the outside tire.

Getting a decent camber curve on your struts will help everything. It will mean that your inside tire gets positive camber on acceleration (which is what you want), it will cut down on understeer, it will mean you don't need as much static camber to keep the outside tire from rolling over.

I was very happy with a no-bars front or rear setup on my slightly heavier, slightly lower track car.

Awesome, thanks DoD. Since this car is my DD for now. Not sure if my passengers can handle a higher spring rate yet. Maybe I should pay up for the corner balancing and try disconnecting the front bar?

Give it a shot. You can tune roll resistance with ride height. With a strut suspension up front, higher = less roll. That said, if you keep the spring rates you have now, I think you'll probably need to keep the stock bar installed. Hell, try it both ways. Everything I'm telling you is based on a completely different car.

How much more worn is the inside vs the outside? Can you give us some measurements or post pics?

I'll try to take pics next time but from memory it was like 1/32" on the inside and 3/32" on the outside.

I also just had a realization that I should have brought up earlier. Since my car is FWD and I'm slowly building up the AX mods, for AX I have just two wheels with ZII tires. That wheel set is mounted from the front when I'm AXing. The car being FWD, all of the action is in the front and the rear rarely sees any wear when I autocross so I just leave my DD set on there.

Anyway, the point is, the only ZII size that would fit the Abarth was a 17" tire. So I have 17" ZII tires in the front and 16" RE-11 tires on the back.

The 17" tires have a diameter of 23.8" and the 16" tires have a diameter of 23.2". I set the Bilstein's height based on Axle to Fender distance (F: 12.5" R: 12.9"). Technically the Axle to Fender distance should be close regardless of wheel/tire diameter. But the way the tires behave with different diameters, I'm guessing is different.

So with the 16" tires, the front of the car is .8" below the rear of the car. With the mixed tires, the front of the car is .2" below the rear of the car.

Mentally picturing the front of the car being higher than the rear of the car, I can mentally see how that would wear the inside edge more. Granted the weight distribution is 64/36 stock, stock Axle to fender settings are also 1" different front to back.

So the combination of the coilovers being set closer front to back and higher tires on the front, means the weight distribution is more on the rear, leading to less grip on the front tires and wheel spin.

raising/lowering a car can mess with the toe settings

If you measure the toe and it seems good, might part of the problem be bushing flex causing dynamic toe out?