How many HP is needed at the axle of a semi truck?

Rating HP at the axle depends a lot on the type of engine, trans and gear ratiOS of the rear ends. Most over the road trucks today will have any where from 300 to 450 HP at the rear wheels.

The truck I own and drive has a C-15 550Hp Cat with a 13 speed trans and 3.36 rear ends.

The ECM had been reworked and it now puts out almost 800Hp at the flywheel giving it 675Hp at the wheels