How exactly do the different gears on a bike change how easy it is to pedal? And why is it that despite being at the appropriate gear, it is still harder to climb uphill despite the same pedals per minute?
In: Physics
It’s essentially the same concept as a lever: you can perform the same work with a lot of force over a small distance, or a smaller force over a longer distance. (Ignoring the fact that it’s often easier to maintain a higher power output with a moderately fast cadence)
However, the total amount of work needed to climb a hill doesn’t change.
Imagine a gear with 5 teeth. It takes 1 full rotation to turn a gear with 5 teeth. Now replace that second gear with one that has my teeth. It takes 2 full rotations of that gear to make that same distance turn. Flip it around so that the 10 tooth gear is turning the 5 tooth gear. Now it only takes half a turn of the first gear to spin the second all the way around. Smaller gears turn more quickly, but generate less force. Larger gears turns slowly but generate less force.
When we go up a hill, we are working against gravity which wants to pull us back down that hill. It takes more energy to do that whether we are using the gears to make many quick rotations, or one slow rotation.
A very basic answer is when the front gear is very small and the back gear is very big it will take (this is just an example) 5 pedal turns to turn the front to make the back spin once, resulting in more torque/pushing power like what you need going up hill.
Reverse that and you will have more speed because the front is spinning once and the back is spinning 5 times but you sacrifice the torque/pushing power, this is what you would use on a flat surface.
One issue going uphill is that if you try to remain seated your body position changes to adjust to the bike slope vs gravity and your muscles aren’t working as effectively because your at sub-optimal positioning. Moving to standing helps some, but unless you’re going fairly slow this also adds air resistance.
The other issue going uphill – cycling works as well as it does because on flats there is relatively little resistance to overcome until you’re going pretty fast. The required work rate to go at a decent running speed is very low. Once you’re fighting gravity also the work rate to maintain the same speed increases dramatically, so you have to slow down a lot more than you’d expect for a hill climb.
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