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... spoiled Cali racers[Putting warmers on] 30-45 minutes before a race is the norm for Dunlop, Michelin and Pirelli DOT race tires. Michelin's prefer to leave the warmers on them all day long. Come in from the track and turn them back on. Dunlop's just require you to come back in from a practice or race and just throw the warmers on, but don't plug them in, unless you next race is a couple hours away, and then only about 15 minutes prior.
In the cold and damp, Michelin's suck. They don't keep the temp in and slide all over the place. Dunlop is a much better tire in both dry and damp conditions. Pirelli is better than Michelin's, but not as good as the D209 Dunlop.
All this so the first warm up lap is a comfortable one.
On a side note, I also recommend buying a shock warmer. Gets the shock up to operating temp before you go out and then keeps it at operating temp all day long. Prevents what most people consider low slides due to "cold" tires or "cold" track, when in fact the rear shock isn't at operating temp and it's the lack of rear suspension that causes those low slides.