What is the fastest street legal semi-truck?

Answer 1

The speed of a semi truck is determined by the powerplant, transmission, and rear end gear ratios. Take three trucks.. let's say, in this case, three Freightliner Classic XLS... they have the same motor, same transmission, but different rear end gear ratios. One truck has 3.36 rear ends, one truck has 3.70 rear ends, and one truck has 4.11 rear ends.. the truck with the 4.11 rear ends would be the slowest of the three, but better suited for particularly heavy loads. The truck with 3.36 rear ends would be the fastest.

The fastest truck I've ever driven was a Peterbilt 389 with a Cummins Select 600 horsepower motor, 13 speed Eaton Fuller transmission, and 3.25 rear ends. It was capable of doing over 140 Miles Per Hour.