Help explain this track tire wear

Two weekends ago I was at Mosport for the weekend instructing with the BMWCCA Trillium chapter in my 84 BMW 525i. This was my first full weekend on these Hankook RS4 (225/50R16 mounted on 16 x 8" wheels) but they had another day in the dry there back in June. In between there was street driving and a few autocrosses. This most recent weekend I shared my car with my Dad so it had  extra (although not as hard) sessions while he ran it in the school Saturday and Sunday. All told looking at my fuel tracking app we put 650 km on it over 3 days on track with roughly 40 of those km spent driving around the paddock and to the nearest gas station and back. I drive the car to the limits of the tires (I would probably argue the limits of these tires are higher than most would say) with a decent amount of slip angle. I am not easy on them, the usual question after someone rides with me for a session is "what tires are you on" and they are surprised with the answer. I have had many sets of RS4 over the years.

Anyways, to the problem. Both rear tires look great, like they barely touched the track. Front left is okay, there's a decent amount of wear just on the outside shoulder of the tread and a bit on the inside shoulder. Front right is the issue, it looks fine except for the inside shoulder which is wore to the point wear the tread there is gone on the first 3/4" of an inch in. 

This track has 3 high speed sweeping right handers where the front left is stressed (1, 3 and 8) and two over the crest, down the hill fast lefts (2 and 4).

Alignment is 0 toe and about -2.5 degree negative camber in the rear and 1/8" toe out (measured with my 2' long toe plates strapped to my wheels) and about -3 degree negative camber in the front (I would guess front right night has 0.25 more negative than front left, I should correct that). I run 36 psi hot front and 34-35 psi hot rear. I was not diligent about checking this Saturday/Sunday as I was more focused on my student and my Dad was doing most of the driving but was on top of it Friday.

My theory is through the right hand corner just the inside edge is seeing any load on the front right tire while it is dragged across the track and this is the cause of the extra wear on just that tire. If it was a toe issue I would see it pop up on both front tires. 

What do you guys think?

Going forward I need to be way more diligent about rotating my tires to even out wear. I also need to get the temp gun out again and stay on top of that. Maybe for Mosport I should run just a hair less negative camber on the front right as well?

I'd post some photos but it doesn't look like I can upload them at the moment.

And shameless plug but here was my best lap there last year and representative of how I drive the car.

Here's a close up of the car in turn 10, this is what I am basing my theory for the wear on.

I think your assessment is about right and that's kind of just what you get. The more trailbraking you do the worse it will be as you're then trying to use that 1" strip of tire to brake with. That's the one bit of unusual wear that the tires on my cayman get. The rear does it a tiny bit but the front is very noticeably wiping the inner ~1" of the tire. If the car and tires are otherwise happy I don't think I'd be making any substantial setup changes, just be a bit more on top of tire rotations to even it out.

Am I missing it, or is there a pic of the tire?

What are your tire temps?

34 hot psi I about as high as I would go with rs4. Beyond that and they are just getting squirmy and hot.

Tire pics won't post as they're jpeg's and the site doesn't seem to like them at the moment. Looking at the pics both fronts show similar wear, just that the right front is noticeably worse than the left.

Car is around 3000 lbs, forgot to mention that.

I'll get back on checking tire temps again and definitely rotate throughout the weekend. I guess I've had a good run with very even tire wear so I got a bit lazy. In the past I'd just run Saturday and Sunday in a weekend but now I'm running on the Friday and getting a lot more track time.

Left front - you can see the tread go right to the edge on both sides although it is almost gone on outside edge

Inside                                                                                                                                                                                                         Outside

Right Front - tread completely gone on inside edge

Outside                                                                                                                                                                                                                     Inside

Your assessment is spot on. Additionally the inside edge is getting really hot and the rubber is being cheese grated off even faster.

I encounter a similar thing with my Datsun  on the rears.

So if that is the consensus would a toe change help? Maybe go to 0 toe in the front so that inside tire isn't pulling so hard on that bit of rubber?

I'll be back there in a month and I'll have time to experiment provided the track is dry on the Friday and not 0C lol

Having run RS4s on our endurance cars for years, where we usually get 3 races from them (so close to 3k track miles, and they usually age/heat cycle out) I think you have too much camber.  I'm surprised at how little camber we need with these, based on probe pyrometer testing and even wear.   On  our two FWD cars, we only run about 2.2 degrees negative and have good even temps across the tread, and with 1/8" toe out we still wear the inside half down more than the outside half.   Agree with the recommendation of no more than 35psi hot.  

I'd say rotating the tires and even flipping them on the wheels would be the solution

Sonic said:

Having run RS4s on our endurance cars for years, where we usually get 3 races from them (so close to 3k track miles, and they usually age/heat cycle out) I think you have too much camber.  I'm surprised at how little camber we need with these, based on probe pyrometer testing and even wear.   On  our two FWD cars, we only run about 2.2 degrees negative and have good even temps across the tread, and with 1/8" toe out we still wear the inside half down more than the outside half.   Agree with the recommendation of no more than 35psi hot.  

I think this is likely the underlying issue. Up until this year I was running a different set of coilovers and the most negative camber I could get with them was around -2.2 range, tire wear was always pretty good with the outside going just before the inside. This past winter I welded up a new set and offset the struts to give me more negative camber and set them to around the -3 range. First two track events I didn't get a lot of driving at as I was doing our ITS and there was wet weather mixed in, this event was dry and the car barely stopped. 

I think I'll take out some camber (-2 to -2.5 ish) and leave my toe at the same setting as it is now (1/8" out) if I am running RS4 for the next event, I'll also try a bit less pressure. I also have a set of Toyo RR mounted on another set of wheels to try, I think they'll want a setup closer to what I have now so this all could be weather dependent.

I might pickup two extra new tires to match with my very nice looking rears. The two current fronts could go with a pair of old rears that are almost done. I have lots of 16 x 8 wheels to play with and a friend has the tire machines.

Thanks of all the feedback

With turn 2 being off camber I don't see the tire mostly running on the inner edge and turn 4 while being visually scary to drop over the crest doesn't really load the tire that much.

 Maybe have a good look at your bushings,I wouldn't be suprised if you have one allowing movement when loaded.

 We endurance race there and that place is by far the easiest place we've raced on tires.

1/8" toe-out seems like a lot. Most of the cars I've tracked 1/16" was the max toe I ever ran, but then I never ran a 5 series taxi cab. 

kevlarcorolla said:

With turn 2 being off camber I don't see the tire mostly running on the inner edge and turn 4 while being visually scary to drop over the crest doesn't really load the tire that much.

 Maybe have a good look at your bushings,I wouldn't be suprised if you have one allowing movement when loaded.

 We endurance race there and that place is by far the easiest place we've raced on tires.

The tire I have the issue with is unloaded in turn 1,3 and 8 (also 5 and 10) where there is a lot of load. In the front of the car it is all spherical joints where the bushings were but that doesn't mean there isn't a problem. The car is up in the air right now so I'll check that out along with the ball joints for sure. Thanks

I'd recommend trying zero toe on the front, that's what I run on my Toyobaru and AE92. I used to run some toe-out on the AE92 when it had a slower steering rack but I found that it wasn't helpful anymore with the 2.5-turn rack, and toe is generally a lot harder on tires than camber. I suspect that camber is at least half of the problem around Mosport though.