Race car drivers do weave, and they are trying to heat their tires. However, the object of weaving isn't to warm.

If you've ever seen a set of racing tires close up, you know how different they are from the tires on your family car. Racing "slicks" are just that, treadless tires. But they're not totally slick. The manufacturing process does leave some rough spots and a couple of slow laps scrubs the roughness and debris off the surface.

Equally important, tires aren't at maximum grip when cold and those first slow laps warm them up enough so that they do their thing when up to full speed--like in the nanosecond after the green flag drops.

When you see drivers weaving their cars back and forth, they're also testing to see exactly how the tires grip the surface, how the tires are setting up on the car, how the car is handling with these tires through the track. Sometimes a little suspension adjustment is needed as well; the driver can make that tweak from inside the car.