NASCAR Racing: racing, debris, tires

Question
before nacars start to race, why do they zig-zag in and out?

Answer
Hi Joyce,

The tires on the cars come brand new.  They cross in and out to clear the debris off of the tires.  This leads to increased grip to the track, the only time this would not be helpful is when they have had the same tires for a while.  Of course, wearing them out wouldn't help anything then!
Hope i helped.
Coy Jordan