Why do dragsters have large back wheels?

Answer 1

Most of the weight of the dragster (or rail job, or whatever) has been located at the rear so that the rear wheels get the most traction that they can. Since there is relatively little weight on the front wheels, they can be lighter duty than, say, a stock motor vehicle. A narrow wheel and hub will serve for the light load, and a narrow tire inflated to a high pressure has a low rolling friction compared to an ordinary auto tire. The hub bearings can be light duty and low friction as well, all adding up to lower rolling resistance and lower elapsed times for the dragster.

Answer 2

1) aerodynamics 2) to keep car from flipping over 3) provides safe place for fuel tank

Answer 3

they are wide and tall for traction, higher and wider tires increases the tire patch(foot print in contact with the track).

Answer 4

Notice that they are also very low to the ground. All of this helps them stay on the ground.