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Here's some info that was shared on a 125 site about Dunlop race tires. Some of it is 125 specific, but much of it apllies to other tires.
This DOES NOT apply to street tires.
Here are the long awaited factoids that I learned from Steve Brubaker at Race Tire Services (Dunlop's distributor East of the Big Muddy). Much of this, many of you already know, but there may be some interesting details:
1. Dunlop does not recommend an optimal heat range for 125 tires. Steve emphasized that it is more important that you have proper tire pressure (27, I recall) front and rear, than to let air out just to increase the temp. (My experience has been that at cool tracks, I've run 24 or 25 with good stiction!). He feels that when people let air out, the bike just handles funny.
2. Nitrogen is an acceptable substitute for air. It's more stable because it holds less water, which is what expands when heated.
3. 10% higher pressure when warm is a myth. DO NOT GO BY THIS! As previously mentioned, air holds differing amounts of water depending on the source. As many of you painters know, compressed air creates moisture. So, actually, a "bicycle pump" would give you more stable air. (I tried nitrogen last year and didn't notice much real difference, except my credit card was warmer and it's a biotch to load and unload in the van! Surprisingly, I still noticed a pressure increase when warm.)
4. Much discussion about heat cycles. Steve feels, and I concur via experience, that the real tire killer is rapid cool-down. What this does is brings the tire's inherent oils out to the surface (ever notice "bluing"?) and makes the rubber carcass less elastic. Picture a hard skin forming on pudding made the "old school" way. His advice is to get the unplugged tire warmers onto the tires ASAP after coming in. The warmers themselves act as insulators that let the tire cool down more slowly - so, too bad for those folks that have to do post-race tech!
5. What about tire warmers? Well, Steve likes them, if used properly. Only plug them in 30-45 minutes before use. Leaving them on longer is just cooking the performance out of them. (I've heard it rumored, but not scientifically confirmed, that you have more heat in your tires right off the warmers, than you do as the race progresses. Bickle says that you've got the first three or four laps to be a hero.)
6. How long do tires last before the performance drops off? Steve says that hotshots like Miguel DuHamel use tires only twice, then bin them. He also says that a guy like me in his first year can use them down to the wear bars - which is a WHOLE season! He says that performanc drops off dramatically in the first two short sessions (or in one long race) as they lose 5%-10% in these first two cycles or in a long race, then levels off to a straight line gradual descent over time.
7. How long does it take to "scrub-in" new tires? One decent lap, Steve says.
8. What do I have to do to get the "release agent" off the outside of the tire? Nothing. Dunlop does not use a release agent. DO NOT USE BRAKE OR CARB CLEANER ON THE TIRE, AS IT WILL BREAKDOWN THE STICKY COMPOUNDS! Use them straight up!
9. What's the deal with "cold tearing"? Steve says that cold tearing happens both with a a cold tire on hot tracks as well as a hot tire on cold tracks. Temperature differential creates a desire in the rubber to attach to the track, instead of itself.
10. Got gummy balls? Forget Tinactin. What's happening is that those little gooey balls on the edge of your tire are from the track, not from your bike. They mean nothing, except there's a lot of rubber on the track.
11. What compound to use? That's up to you. Ostensibly one uses a harder compound for higher track temps. I generally use soft, but might begin to play with mediums just for comparison when it gets hot and sweaty out.
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I'm sucking in the info around here. I got a billion questions but I don't want to be posting 6 topics a day, I'll figure it out on my own or ask around up at the track.
