Not all the advantages, however, are with modern bikes. Acceleration is thrust, divided by weight, so light bikes like the middle-period 500cc two-strokes could accelerate really fast even though they developed “only” 150 horsepower. Before the 130-kilogram weight minimum (286 pounds), a few 500s weighed less than 250 pounds. That, plus a 170-pound rider and 30 pounds of fuel added up to 450 pounds, or about 3 pounds per horsepower. Today’s Superbikes are about 100 pounds heavier, giving a 205-horsepower bike 2.75 pounds/horsepower—not all that much more. Of course, MotoGP four-strokes, with a bit more power, look even better.