Interesting tire degradation with BFG R1 S
 

Here is my car as it sits now:
BFG R1-S tires at 35.5 psi hot
Stock suspension
DTC-60 pads
Togue Factory brake ducts
Motul RBF-600 brake fluid
Camber plates
2.6* of front camber
1.3* of rear camber
The car is pretty much stock other than that, and I do the pedal dance before pulling onto the track.
Recently I was at High Plains Raceway and noticed something funny with the tires. It was my first day on these tires. They are four years old and have been heat cycled by The Tire Rack. Before yesterday they had maybe one or two sessions on them. In the morning ambient temps were in the upper 40s. By the end of the afternoon it was around 70.
I experienced some graining with the front tires. Once the car had warmed up about three or four minutes and I started building some speed, the front tires would start to feel like they were driving on small gravel pieces. They would sound louder and rougher and I could feel it through the steering wheel.
When I brought the car in I could see a strip of clag all the way around the inner third of the tire, but the outer two thirds of the front tires looked perfect. The wear on the outer and inner shoulders looked right where they should be.
There were two turns where this behavior was especially noticeable (7 and 11). They are both very long turns. I would enter the turns with almost none of this bad feeling from the front tires, but as I would drive through each of these long turns, I could slowly feel them graining. By the end of each turn it feel fairly rough in the front end and the grip would slowly go away as I proceeded through each turn. By the end of these turns the car would be understeering significantly.
It seems to me like these long sustained turns heated up the front tires past the point of where they should be. That said, these are pretty serious tires and I would not expect that type of driving to be a problem for them. Especially on my lowly car with lower ambient and track temperatures.
I measured temperatures on the inner shoulder, center and outer shoulder of each tire at the end of a session. I came into hot pits quickly, stopped quickly and jumped out to measure as fast as I could using my cheap China Freight IR pyrometer. Each of the four tires varied less than ten degrees across the tread. IIRC most were about five degrees in variance.
I don't have data acquisition available for review. If you need to see a video of my driving i can post one, but doubt it's necessary to figure out what's going on with the tires. I've been driving on tracks for 17 years and instructing for much of that.
FWIW, I spoke with a long-time national champion racer about this yesterday at the track and he couldn't figure it out.
What theories do you guys have for this kind of tire behavior? I'm kind of drawing a blank. My only theory is I need more camber up front, but honestly, I don't really think that's right based on tire temperatures.
CSG Mike already responded in another thread (thanks!) saying that he thinks it's just the nature of the stock suspension causing the car to understeer and therefore overwork the front tires. What other thoughts do you guys have?
TIA

Sure sounds like an overheated front tire.

I ran R1Ss in autox for the last 3 years on my 240. They like/will deal with heat better than the hoosiers, but still fall off at some point. The S is the autox compound so I'm not too surprised that they're overheating on the track.

Also we ended up running really low pressure on my 240, though I use 245s that are a bit stretched onto 9.5". That plus -3.6* of camber or so in front. But I think we ended up down to like 23 or 24psi which is where they seemed to work best in terms of feel and how the tire looked.

Very timely thread - I had a similar thing happen last weekend at the track and wasn't sure what it was. Felt like the car was running over small pieces of gravel in turns.

I had just mounted new 2013-stock BFG Rivals and thought it was from the extended tread blocks on the shoulders. From your post I gather the vibration was actually a result of graining/clag. Good to know. Didn't think it was that because I don't remember feeling it on my last set of tires (Nitto NT05) even though the amount of clag buildup looked roughly similar.

I noticed we're both running on stock suspension and 3-4 year old tires. I think those may be factors. I've only got -1.5* camber in the front so my setup is even worse than your's. I did notice significant wear on my front shoulders after 8 sessions (2 days) on these tires. Ambient temps were 55 F. I was running 42 PSI hot in the front to try to stop some of the shoulder rollover. I know I definitely need some more camber or stiffer suspension, or both ideally.

BTW if the strip of clag built up around the inner 1/3 of your front tires, doesn't that mean you would benefit from even more front camber? Something in the -3.0 to -3.5 range? Just a thought.

Thanks for the response, DS. You said your car, "Felt like the car was running over small pieces of gravel in turns." That is exactly how mine felt. Could you tell it got worse toward the end of long-radius turns that took a few seconds to get through (as tires heat up)?
I don't know if clag on the inner third means that I would benefit from more camber. It wouldn't surprise me, but I just don't have the experience to know.
This is certainly interesting considering the age of our tires and stock suspension, huh? Thanks again for sharing your experience. I'm looking forward to hearing what others think.

I would start by checking with BFG what the recommended temperature for that compound is. Then I'd get a probe pyrometer and check again - "cheap IR" doesn't provide a lot of confidence in temperatures besides yes it's hot, no it's not. http://www.longacreracing.com/techni...aspx?item=8159

Graining is usually caused by low temperatures, not high temperatures. Some exceptionally soft compounds will grain no matter what. Given that the "S" in R1S stands for "sprint" it's probably a very soft compound even if it is 4 years old. My BFG Rival S (which I've heard rumors that it's the same or close to the same compound as the R1S) had some graining no matter how hot I got them, even when they were literally painful to touch; graining got better as temps went up though.

The other thing it could be is OPR. This is usually pretty obvious if the rubber buildup on the tire is a different color shade compared to your tread, or if it is a lot of rubber (do you have pics?). I would actually suggest this is the most likely cause, if you have enough rubber buildup to actually make it rough to drive it's probably not coming from your tire or you'd be out of tread. If turns 7 and 11 are the most punishing, that is where most of the OPR will be...

It's possible it's a combination of things - you could be overheating the tire momentarily in those long turns while picking up OPR and making it rough to drive.

Yeah it was particularly noticeable in two ~80 mph right sweepers. The shoulder of my LF tire took a beating - it's worn about twice as much as the RR. I guess it makes sense that rubber formed enough clags that it could be felt behind the wheel.

Thanks, renfield90. Yes, it is a sprint compound. Everything I've read has said they get better as they get hotter. That's why I'm so skeptical that I overheated them.
I didn't realize graining is normally caused by low temperatures. But if that's the case, it makes sense. Generally track days around here are in the 80s and 90s, not 50s and 60s like I experienced. I would love it if that solved the issue.
However, it seemed like the harder I drove the worse it got. And, I was driving harder in the afternoon when ambient and track temps were warmer. That makes me think the graining is not from the colder temperatures.
I hadn't even considered OPR. Interesting theory. There was no difference in color between the clag and my tire. I don't have pictures right now, but there is enough on one of the tires to have a continuous string ~1/2" wide around the entire tire. Of course there are bits and pieces elsewhere, especially on the inner third, but it's not like it's a slab three inches wide.
Thanks again for the input. I've been trying to contact the right person at BFG but it's not easy. God I hate what customer service departments have turned into.

Yeah, band of rubber is OPR. That's not the tire coming apart.

Are the turns significantly off camber?

No. In fact they both have significant camber.

Different color is a dead giveaway for OPR, but same color doesn't rule it out.

Could be more OPR than normal due to temperatures? The other guys will also suffer from low tire temps and might be laying down more rubber than normal due to more sliding.

From Tire rack

I wouldn't think that 70 degrees was all that hot but the issue you call graining I have experienced in heavier cars when the tires overheat. It sounds horrible like your walking on snow and the car pushes severely through any turn. Usually you will see wear on the outside shoulder though. Have you tried taking temps when this happens?

It sounds like we are all on the same page regarding the sound and feeling of what I experienced. I didn't see unusual wear and temperatures were consistent across the tire. Remember, it's a pretty light car with 2.6* of camber in the front.

Can we get some pics please?