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I'm wondering what everyone is experiencing regarding heat-cycling of the rear SC2 tires on track. Here are my observations, as I finish off my third set of rear tires:
- The tires heat-cycle out long before the tread is gone.
- The main evidence of heat-cycling is pronounced drop in rear grip, making the car loose and slow. The rubber does seem to become less soft, but not really hard.
- As the cycles accumulate, reduction in grip is gradual, then the grip falls off quickly during the last cycle or two. So there's not much prior indication that the tires are nearing the end.
- Seems that I'm getting 6 to 10 decent days out of the rear tires, depending on the number of cycles per day, so maybe about 25-30 cycles (I haven't been counting cycles, and may need to start doing that).
Trakcar toasted three sets on our little ED escapade and was well into his forth set too... We found that there was a gradually degradation after a certain number of heat cycles but the outer shoulders on the rears were chunking and fried before/or as we got to the point of significant grip loss on the RS. Inner half of the tyre showed only reasonable wear. Longevity seems significantly improved in terms of HCs compared to the MPSC1s that came standard on my 997.2, hated them. Will be trying these on mine next!
Trakcar toasted three sets on our little ED escapade and was well into his forth set too... We found that there was a gradually degradation after a certain number of heat cycles but the outer shoulders on the rears were chunking and fried before/or as we got to the point of significant grip loss on the RS. Inner half of the tyre showed only reasonable wear. Longevity seems significantly improved in terms of HCs compared to the MPSC1s that came standard on my 997.2, hated them. Will be trying these on mine next!
How did the wear and heat-cycling compare between the front and rear tires? And do you know whether he had the N0 vs N1 spec tires?
Part of my reason for posing the question is that I just had a track alignment and setup done on my GT3 which has worked well for others, and I'm trying to interpret the before/after results.
Before the alignment/setup, I tracked the car two weeks ago, and found the grip and balance of the car to be good during my last session. At the same event, I drove another 991 GT3 with the same tires, Crawford wing, and different alignment, and it felt similar to my car.
Then I got the setup done and tracked the car yesterday, and right out of the gate I found the car to be loose. It's not loose in the sense of snap oversteer (rotation and movement of the rear are slow enough to be manageable). The car will oversteer with too little or too much throttle as expected, but even when the amount of throttle is within the acceptable window, there's just a lack of rear grip. Peak G forces from the car's meter are 0.2-0.3 G below what I normally see, and exit speeds from some corners are ~5 mph lower (huge difference!).
So I'm trying to figure out whether the reason is (a) alignment/setup is too loose, despite working well for others, (b) tires heat-cycled out abruptly (could the grip drop during the 2 weeks between the events due to a long-term effect from the previous heat cycle?), or (c) combination of (a) and (b).
When my previous two sets of rear tires heat-cycled out, I did see a big drop in the grip over the course of one or two sessions, and then the car felt similarly loose, so that supports the heat-cycling hypothesis. But I'm still surprised to see such a big drop in rear grip from end of one event to beginning of the next event, and the setup did change significantly between events, so there's also the possibility that the tires still have some life and the setup needs to be changed.
Part of my reason for posing the question is that I just had a track alignment and setup done on my GT3 which has worked well for others, and I'm trying to interpret the before/after results.
Before the alignment/setup, I tracked the car two weeks ago, and found the grip and balance of the car to be good during my last session. At the same event, I drove another 991 GT3 with the same tires, Crawford wing, and different alignment, and it felt similar to my car.
Then I got the setup done and tracked the car yesterday, and right out of the gate I found the car to be loose. It's not loose in the sense of snap oversteer (rotation and movement of the rear are slow enough to be manageable). The car will oversteer with too little or too much throttle as expected, but even when the amount of throttle is within the acceptable window, there's just a lack of rear grip. Peak G forces from the car's meter are 0.2-0.3 G below what I normally see, and exit speeds from some corners are ~5 mph lower (huge difference!).
So I'm trying to figure out whether the reason is (a) alignment/setup is too loose, despite working well for others, (b) tires heat-cycled out abruptly (could the grip drop during the 2 weeks between the events due to a long-term effect from the previous heat cycle?), or (c) combination of (a) and (b).
When my previous two sets of rear tires heat-cycled out, I did see a big drop in the grip over the course of one or two sessions, and then the car felt similarly loose, so that supports the heat-cycling hypothesis. But I'm still surprised to see such a big drop in rear grip from end of one event to beginning of the next event, and the setup did change significantly between events, so there's also the possibility that the tires still have some life and the setup needs to be changed.
Mate please keep us informed as to what pans out here. Have been awaiting your feedback on super secret sauce geo this week. It sounds like an interesting outcome so far. It actually sounds a bit more like my car before I reverted to factory geo, but to be fair I had a problem early on with heat cycled tyres tho I had no idea they were cycled as I was an early adopter. I think only way you can know is chuck a new set tyres on - have them heat cycled by tire rack first. They will be fast for the first day because new but by day 2/3 you can then make proper call on alignment??
How did the wear and heat-cycling compare between the front and rear tires? And do you know whether he had the N0 vs N1 spec tires?
Hey, Pete's tyres were N1 spec... They roughly wore on par to be honest and they all seemed to lose the outer shoulder, inner 2/3 were decent. Pete was running cambers of approx 3 to counter this. The guys from one of the support teams even commented on how the inner 2/3 were minimally worn and they made toe adjustments on the fly to aid wear.
From what I recall, because of the coarse surfaces on many tracks we drove, tyres would be toast on the outer third before having heat cycled out.
Part of my reason for posing the question is that I just had a track alignment and setup done on my GT3 which has worked well for others, and I'm trying to interpret the before/after results.
Before the alignment/setup, I tracked the car two weeks ago, and found the grip and balance of the car to be good during my last session. At the same event, I drove another 991 GT3 with the same tires, Crawford wing, and different alignment, and it felt similar to my car.
Then I got the setup done and tracked the car yesterday, and right out of the gate I found the car to be loose. It's not loose in the sense of snap oversteer (rotation and movement of the rear are slow enough to be manageable). The car will oversteer with too little or too much throttle as expected, but even when the amount of throttle is within the acceptable window, there's just a lack of rear grip. Peak G forces from the car's meter are 0.2-0.3 G below what I normally see, and exit speeds from some corners are ~5 mph lower (huge difference!).
So I'm trying to figure out whether the reason is (a) alignment/setup is too loose, despite working well for others, (b) tires heat-cycled out abruptly (could the grip drop during the 2 weeks between the events due to a long-term effect from the previous heat cycle?), or (c) combination of (a) and (b).
When my previous two sets of rear tires heat-cycled out, I did see a big drop in the grip over the course of one or two sessions, and then the car felt similarly loose, so that supports the heat-cycling hypothesis. But I'm still surprised to see such a big drop in rear grip from end of one event to beginning of the next event, and the setup did change significantly between events, so there's also the possibility that the tires still have some life and the setup needs to be changed.
I wouldn't make any changes to the setup until you try it with some fresh tires. Too many unknowns with old tires. Looking forward to hearing your impressions.
About to push some old Cup2s to the limit so I can save my fresh Cup2s for a good comparo with the Trofeo at Road Atlanta. I have 32 cycles on the back and am hoping I can make it through this weekend at Barber. I don't know the track very well, so I won't be pushing it.
I wouldn't make any changes to the setup until you try it with some fresh tires. Too many unknowns with old tires. Looking forward to hearing your impressions.
About to push some old Cup2s to the limit so I can save my fresh Cup2s for a good comparo with the Trofeo at Road Atlanta. I have 32 cycles on the back and am hoping I can make it through this weekend at Barber. I don't know the track very well, so I won't be pushing it.
Yup, we decided to leave the setup alone and change the rear tires, and then try to car again this weekend.
With 32 cycles on your rear tires, if your experience fits mine, I'll predict that your rear tires will cycle out this weekend at some point, but it seems that several factors can affect how many cycles we can get, including max temp reached during each cycle (function of track, tire pressures, how hard the car is pushed, alignment, etc.).
Based on some things I read online, it seems that there can also be a post-cycle curing/hardening effect which can last hours to days, but it depends on the tire and I haven't seen any specific info on the Cup 2. If that effect does apply to this tire, that may explain how I went from good rear grip at the end of VIR to low grip at the beginning of the next event two weeks later.
May also be worth noting that I had so much heat in the proximity of the side mufflers that the plastic brackets above the mufflers started melting (photo below). That heat may have contributed to heat-cycling of the tires.
I just changed out a set of Cup2 -- 3,200 total miles, 770 track miles. Still have quite a bit of rubber but I would estimate the tires cancelled out between 600 and 650 miles. I am guessing that was about 25 to 30 cycles, but I don't know as I have not been recording temperatures.
May also be worth noting that I had so much heat in the proximity of the side mufflers that the plastic brackets above the mufflers started melting (photo below). That heat may have contributed to heat-cycling of the tires.
In my experience with about 8 sets of Cup2s, I start to notice the degradation of grip at around 20-24 heat cycles. Tread wear is usually even and is not an issue, with the exception of several tracks that are really hard on tires and brakes. I am satisfied with my alignment (-2.2 front, -1.8 rear), with even wear and even temps as measured with a probe pyrometer.
Interesting thing though is that I always notice the grip degradation in the front first, not so much the rear! I notice the onset of understeer, making it harder to hang tight on the apex, and having to reign in the throttle some to avoid tracking out too far. And as for tread wear, I see more wear in the front than in the rear. Go figure.
11-07-2015, 12:55 AM
Heat-Cycling of SC2 Rear Tires (on Track)
