How do tire tracks help in solving a crime?

There are hundreds, even thousands, of different kinds of tires. Tire tracks are not as unique as fingerprints or DNA, but taken together with other evidence, they can help establish that a person (or, their car, at least) was in a particular place within an approximate window of time.

For example, say you are investigating a man for the rape and murder of a woman. The suspect has a powder blue Ford truck with Michelin C500 tires. A witness saw a woman matching the victim's description get into a powder blue Ford truck driven by a man matching the suspect's description. Tire tracks from Michelin C500 tires were also found at the scene. A cigarette with lipstick matching the victim's was also found tossed on the road, near the tire tracks.

Taken separately, these three pieces of evidence are not particularly damning, but together, they make a pretty good circumstantial case.

Tire tracks are usually just one piece of the puzzle. Prosecutors can easily get a conviction with no more evidence than the DNA from one drop of blood, but you would never get a conviction with no evidence besides the presence of tire tracks matching the suspect's car at the scene.