How many heat cycles are "safe"
 

Still new to HPDE and looking for some advice on when to change out tires. I have a 991.2 GT3 with about 8500mile on it. I've done a total of 6 track days (Thunderhill and Sonoma), which equates to 6 x 5 = 30 heat cycles, or about ~700 track miles. The tires are MSC2's and they look good, still have tread depth, no uneven wear, etc. I have noticed during the winter months (its been "cold" in NorCal this winter) that the tires feel a lot more greasy than they should be.

I'm planning to do another 12 track days this coming summer and was wondering under what conditions would you trigger a new set of tires? Is 30 just too much? does it depend on how hard I use them (the wear is good), or just need to put more time into heating them at the start, or this is just subjective and spend the $ when it feels right?

I just keep using the tires until it starts to cord, usually at the outer edges, regardless of how many days/heat cycles. Sure, the grip degrades way before then, but I'm not that concerned about the fractions or seconds I give up per lap as the heat cycles build up. As far as safety, it's all about knowing the limits, knowing when you're at 10/10th, and staying at 7/10ths.

With the MSC2 I did notice a significant performance degradation, even though there was plenty of tread left I replaced tires once they were gone as track days were not as enjoyable.

I'd be wary of anything past 20 HC on any tire

Really? I've put 24-25 HCs on RE71Rs before I corded them and I'm not easy on tires. haha

My point is that on your question on "safety", safety is about learning where the limits are and staying below them. Using up tires can give you valuable lessons, and DE is the best place to learn them. MPSC's are also pretty forgiving, they do not go from bubblegum sticky to bowling ball slippery. It's a slow/minimal degradation in grip, not sudden. As you have more track days in your belt, you may find that 6 track days and your tires are still looking good means you haven't really been pushing them! ;)

Do you have an extra set of wheels? You've had 6 track days so far, and you're looking at 12 track days this summer. I see you going down that slippery slope, my friend. It's a fun slope, though :) If you don't have track wheels, I strongly suggest you get a set. That way, when you find out that your good buddy with equivalent skills and equivalent car is now passing you, you KNOW it's time to put on the second set of wheels and tires.

In some ways this is a difficult question to answer, in others very easy. Inspect your tires...look to see if any are corded, if there are flat spots, if the sidewalls are cracking. If all looks good, then structurally the tires should be "safe". That said, that doesn't mean they have good grip. They may have fallen off a lot since new, or just a bit. Either way, as long as you're aware of the reduced amount of grip and you're still enjoying tracking that way, then it's not an issue. You might be running several seconds per lap slower on tires with a number of heat cycles vs. a fresh set. But that's also a time where you can learn a lot about how your car handles. And driving at the limit is driving at the limit...it's just that on well-used tires those limits are quite a bit lower :).The problem comes in when you're driving on those tires and still trying to brake in the same way, carry as much speed into a corner, etc. The used tires may not be up to that task and that's the point at which bad things can happen. So I'd say as long as you are aware of the fact that you can't drive the car like you've been driving it, and you won't drive over the limit of what the tires will give you, then you're ok. If you've gotten into the habit of having really good grip and can't adapt to the tires, though, then it's time for a new set.

Also, keep in mind that it's much easier to flat spot a tire in that kind of condition, and it's also more likely you'll have a structural issue of some sort. So if you're worried about something happening early on and losing a track day, definitely make sure you have access to another set of wheels/tires.

+1

Great feedback .. thanks for all the input .. in summary

• I need to invest in track wheels/tires (many sets), trailer, car hauler and a workshop - this is critical :)
• But, basically keep using what I have, until they show signs or physical wear (corded, sidewall, flat spots, etc)
• While doing that ease back on the level of attack to match the tires performance
• If performance gets too low or if physical wear is too high it's time for a new set.
• If you don't want to go through the learning process of tires losing performance just buy a new set at around 6 ish days.

My first day this year is at Thunderhill in April, so probably won't be stupid hot yet, I'm also going to take it super easy since it's first day so will try them out at a low level of attack and see how they feel. They don't show any major physical signs of ware. Then swap out if I don't like the performance, or if the tires are too far worn afterwards.

Couldn't help myself ..
https://cimg7.ibsrv.net/gimg/rennlis...32d2fe4fa4.jpg

Another question - why do folks replace the 20 inch wheels for 19's? I'm seeing very little delta in cost (from tire rack) between them. Is it for cost or performance/safety?

19's - 265/35R19 (Front) & 325/30R19 (Rear)

• R7 = $1915 for a set
• TROFEO R = $2032 for a set

20's 245/35R20 (Front) & 305/30R20 (Rear)

• R7 = $1940 for a set
• MSC2 = $1824 for a set
• TROFEO R = $2232 for a set
• Dunlop = $2006 for a set

With the largest delta the difference is $2232 - $1915 = $317, assuming a set of 19 Forgelines is about $8K you'd need to do 25 new sets of tires before you brake even. Or 150 track days assuming you get 6 days per set (which seems to be the average on the forums).

Are my costs wrong, math wrong, or is there really not that much $ to be saved between 19's and 20's

Lighter wheels and tires plus more rubber so left apt to dent a wheel if you hit a beam. You'll be about to re-coup 60-70% of the wheel cost when you are done with them assuming they are in good shape. Careful, tracking can be fun and addicting (as well as expensive the faster you go).

Thanks for the insight, so performance and durability as opposed to cost savings.

I get the addiction bit, my first two track days were in a GTS, which prompted me to pull the trigger on a GT3, then I did 6 more day last year and I'm already booked in for 12 more this year. I set a "budget" of $20K but, that's almost gone with DE fees, insurance, gas, hotel, service (rotors, pads, brake fluid, alignment, oil, tires).

I will need to talk to the CFO and up the budget. I'd probably go with roll-bar, 6 point & HANS before I went with a dedicated 19 inch set of wheels/rubber, easier to negotiate safety spend vs performance spend.