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I was taking air out of my tires after a session at Lime Rock yesterday when I noticed what looked like a decent sized cut in the sidewall of my rear tire. It was a few inches long and right on the edge of where the tire meets the wheel rim. I wasn't sure what could have caused this, as I hadn't hit anything except maybe smoothly going over some track curbing. I got opinions from a few people and decided that the tire was not safe. So off to Tire Rack I went (1hr 15min to their Wondsor, CT distribution center), bought 2 new rears and had them installed (thanks to Zeller tire in Torrington, CT!).
When we removed the tire from the wheel, we found that the crack actually went more than half way around the bead of the tire. The tire was about to completely come apart! Date code on the tire is 20th week of 2016, and they probably had approximately 25-30 heat cycles on them when I found the issue. Some would say they were reaching the end of their lives anyway, but I don't care how many heat cycles they have on them, they shouldn't be coming apart like this!!
If you're running MPSC2s, please keep an eye out for this. I'm lucky I found it when I did. Could have been a terrible situation.
Hmmm. That article talks about tread splices which, from the illustrations and text, seem to be across the width of the tread of the tire, not the sidewall where my issue was.
This looks like the known issue of going out with pressures too low on cold tires. I had one come off just like that and my tire guys told me that Michelin has been advising that folks should increase initial pressure until the tire is warm or this will probably happen. What were your initial cold pressures?
I actually went out for the first run at pretty high pressures. It was a cold morning, so I kept them at 31-34 to see how hot they would get. They ended up in the mid-40s after one session, so I immediately bled them down to 33, which is where I want them when hot. I kept up the same procedure for the next session, 2 hours later. After that session is when I found the cracks. I probably went out for the 2nd session with the tires at 28-30. This was my first event of the year.
How low is too low to start, according to Michelin?
They told me not to start below 30, but it sounds like you were good on that.
Well I'm SURE I've started well below 30 in past events. How do you start at 30 or above and still keep a decent temperature over the course of a DE session?
If I start at 30, my temps will be high 30s or over 40 by the end of every session. I'd be sliding all over the place. I want my hot temps between 32 and 35...
Well I'm SURE I've started well below 30 in past events. How do you start at 30 or above and still keep a decent temperature over the course of a DE session?
If I start at 30, my temps will be high 30s or over 40 by the end of every session. I'd be sliding all over the place. I want my hot temps between 32 and 35...
Tire rack info agrees with you. Cold pressures of 25-28 and hot pressures of 32-36.
I have. I experience with the tires on my car so just passing on what if found on the interwebz.
30 cold, first session of the day, run them up, bleed off and then they should be fine after that. Apparently overworking cold rubber is the issue. Same thing with other tire brands as well. In the race to build lighter tires they don't cut down on the tread material so they wind up building sidewalls as thin as possible which makes them vulnerable unless treated just so. Delaminating Hoosier shoulder because of rolling over on cold tires is another common example. Toyo R88R have had similar complaints, bubbling sidewalls. You also have to warm tires up properly to avoid these problems. I'm always curious how folks avoid trouble when I see them flying right out of the gate during a session.
30 cold, first session of the day, run them up, bleed off and then they should be fine after that. Apparently overworking cold rubber is the issue. Same thing with other tire brands as well. In the race to build lighter tires they don't cut down on the tread material so they wind up building sidewalls as thin as possible which makes them vulnerable unless treated just so. Delaminating Hoosier shoulder because of rolling over on cold tires is another common example. Toyo R88R have had similar complaints, bubbling sidewalls. You also have to warm tires up properly to avoid these problems. I'm always curious how folks avoid trouble when I see them flying right out of the gate during a session.
That's probably the key. Work your way up to the hot pressures that you want.
I have no idea what caused this particular damage. Glad it didn't fail on you on the track.
FYI, the proper warm up technique is to avoid any lateral load and curbs while the tire is under inflated. Heat it up progressively by accelerating and braking. Also heat them up from the inside by dragging your brakes (if your car does not have an electronic brake/throttle interconnect). Most of the time the damage is done when tires are under inflated and they fail later. I don't have much experience running street tires on a track but slicks we sometimes start as low as 16 PSI and it is easy to damage them. Good drivers can get 50+ deg of temp into their tires during an out lap this way. It's usually harder to get temp in the rears than the fronts.
Thanks for the info, all. I'll take more notice of how I warm the tires up at future events. Maybe it was the cool weather (low 40s), but I found it difficult to get heat into them on Thursday. They took almost the whole session to warm up. Anyway, the more you know...
Bruce - I won't be at Lightning next week, unfortunately. My next event is at The Glen with Zone 1 in May. My marriage (and wallet) can only afford one event per month!
Thanks for the info, all. I'll take more notice of how I warm the tires up at future events. Maybe it was the cool weather (low 40s), but I found it difficult to get heat into them on Thursday. They took almost the whole session to warm up. Anyway, the more you know...
Bruce - I won't be at Lightning next week, unfortunately. My next event is at The Glen with Zone 1 in May. My marriage (and wallet) can only afford one event per month!
Im gonna be at Mid-O while you're at Zone 1 WGI.
LCMT?
04-19-2019, 12:41 AM
Michelin Pilot Sport Cup 2 failure
