Lately I've noticed a lot of my riding buddies buying racetrack takeoffs for use on their streetbikes. They're pretty cheap, at least relative to new tires, so they're a good price bargain. My question is this: Many of them have a blue hue to them, side edge of the tread. I suspect this means the rubber has overheated and is now chemically altered enough that the tire won't stick when leaned over. True? What's the skinny here?

The blue color you see on a tire that's been used on the racetrack is oil that's been released from the rubber. This is a good sign, a sign that the rubber still has oil in it, oil included in the original compound by the manufacturer to keep the rubber flexible, and grip high.

The blue color does not mean the tire is junk, although it's important to remember that the tire in question will not stick as well as a new tire. A tire's best grip occurs the first time it's gotten up to temperature; for a race tire, that's the first several-lap session it's used. After that, grip falls off. So, tires with a blue tinge, as long as they have plenty of middle, section tread remaining, should be fine for normal or even semi-aggressive street use.

But because the tread on the extreme edges is usually mostly gone, they're not as good a bet for track-day use.