Re: Get-me-home advice - stripped crank
Posted: Fri Jan 08, 2021 3:33 pm
My understanding is that it's not to do with how force would be applied if you held a spanner on the axle and turned the cranks, but to do with the way that forces are applied to the axle and where it threads into the crank.
One way to think about it is rolling a smaller cylinder (e.g. a magic marker) around the inside of a larger cylinder (e.g. a mug). If the smaller cylinder turns anti-clockwise, it will move around the larger cylinder in a clockwise direction (and vice versa).
This counter-application of forces applies to the pedal axle. If you consider your foot pushing down on the pedal, the axle effectively pivots where it enters the crank arm, so is pushing up on the crank threads. It's by this mechanism that the forces applied by the pedal axle to the crank arm are opposite to the way to the pedalling direction. It's this counter-rotation that has the effect of stopping the pedals coming unthreaded from the crank arm.
One way to think about it is rolling a smaller cylinder (e.g. a magic marker) around the inside of a larger cylinder (e.g. a mug). If the smaller cylinder turns anti-clockwise, it will move around the larger cylinder in a clockwise direction (and vice versa).
This counter-application of forces applies to the pedal axle. If you consider your foot pushing down on the pedal, the axle effectively pivots where it enters the crank arm, so is pushing up on the crank threads. It's by this mechanism that the forces applied by the pedal axle to the crank arm are opposite to the way to the pedalling direction. It's this counter-rotation that has the effect of stopping the pedals coming unthreaded from the crank arm.