[Chris Williams]

Another way to look at it:

Bracket racing: you call the number you're going to run. A full tree is used to allow for the handicapping at the tree. The delay timer is in the tower.

Index racing: everyone runs the same number. This allows for a pro tree, and the handicapping happens on the track. The delay timer is in the car.

In both forms of racing, there are only two parts of the race that are interesting: the tree, and the finish line. You can't tell who's winning mid-track.

Hope this helps,
Chris