Why are pit bike wheels rear smaller than front? What would is the affect of putting on two tires same size?

Why are pit bike wheels rear smaller than front? What would is the affect of putting on two tires same size?

Why are pit bike wheels rear smaller than front and what would is the affect of putting on two rims that are the same size?

for example: Two 10" rims, 12" or 14 " rims? How would affect the way a pit bike rides, the speed and the jumping or popping?Why are pit bike wheels rear smaller than front? What would is the affect of putting on two tires same size?
Putting a larger wheel on the rear slows acceleratrion for a marginal gain in top speed and raises the rear seat height 1/2 of the wheel difference.Why are pit bike wheels rear smaller than front? What would is the affect of putting on two tires same size?
As with dirtbikes, More tire surface area to the ground for steering traction.

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