NASCAR tires look completely bald, but that's not because they are worn out. It is by design. On a dry track, tires can generate more traction if more of their sticky rubber is in contact with the ground. Putting a tread pattern on the tire helps in wet weather, but in dry weather it is better to have the whole tire touching the ground. That's why NASCAR races stop whenever the track is wet.
Link: http://entertainment.howstuffworks.com/nascar5.htm On the road courses at Sonoma and Watkins Glen, each team has at least one set of rain tires. You wouldn't kill yourself if you ran in the rain on a road course (you probably would if you did it on an oval), so the protocol for rain is to throw the yellow, get everyone in and change to rain tires. I'm not sure if they ever have done it, but they can.
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Those tyres are called full wet weather tyres or full wets. They are heavily grooved tyres that can provide maximum grip even under heavy rain. There is also a slightly less grooved tyre called the Intermediates which can be used under conditions of light rain or drizzle. Full wets are significantly slower than intermediates which are slower than the dry tyres or slicks are they are more commonly called.