Hi Happy,

Discounting slippage, bicycle A has a 1" roller, which spins a 26" tire at a 26:1 ratio. Bicycle B has a 2" roller/26" tire with a 13:1 ratio. What Dave meant is that bicycle B would have less mechanical advantage and has to work harder to move the bike at every speed.

Say that an engine has peak torque at 4500 rpm. That's where it feels most powerful. At 26:1 ratio, Bike A feels this power at 13 mph. At 13 mph, Bike B spins at 2250 rpm, or idle speed. However, it would not have the low end power to reach 13 mph, much like a car being in 4th gear. You would have to pedal faster than 13mph before Bike B could weakly push itself forward.

At 9000 rpm, Bike A is screaming at 25 mph, while Bike B is at peak torque at 4500 rpm. At 9,000 rpm, Bike B will be screaming at 50 mph.

So the larger diameter the roller, the more the engine has to struggle at low speed, but the bike would be faster, but not quicker to 50 mph. The smaller spindle will peak at a much lower speed, and will feel perkier until it begs for mercy at 25 mph.

hope this helps.

5-7