Originally Posted by
LarrySellerz
Hey guys, I recently got a single speed and its gear ratio is crazy low at 42x18. This seems lower than most riders, the fixie kids would laugh at me. My first thought was to up the ratio, but im having to spin super fast in order to keep up on the group ride and I wonder if this is good training, I kind of think it is. Does anyone else run a low ratio like this for training purposes? they say spin to win...
Something we discussed recently in this forum is the internal work required to move your legs and feet up and down as you pedal. Your body has to do both the (usually bigger) external work of pushing the pedals plus this internal work.
Turns out that the internal power requirement is independent of the external power delivered to the pedals but strongly dependent (as we would expect) on pedal RPM. This makes sense because it’s just the work we have to do to move the mass of legs, feet, pedals and cranks around as we pedal.
So, we spend more W/kg spinning our legs fast than we do spinning them slow. For example, at 110 RPM, the internal work runs about 1 W/kg, which is already significant and it is a sharply increasing function at this point. By comparison it will only be about 0.1 W/kg at 50 rpm.
So, in addition to protecting knees from greater forces and strain, you will also work your body somewhat harder at a higher cadence (for the same actual speed on the bike).
Otto