How does Hill Climbing Work?
Discussion
I was grinding my way up a steep pitch today, huffing and puffing but feeling quite pleased with myself, when it crossed my mind that a 'proper' cyclist would probably have passed me very easily and a Pro would have left me for dead ages ago.
Now I'm a porky old fart who cycles around for fun and errands on heavy bikes, wearing normal clothes and not even bothering with toe clips, and I realise that the key to getting up hills faster is being fastened to the pedals so you're not solely dependent on your weight pressing down on the pedals, but the more I thought about it, the more confused I got.
How do the physics of it actually work? I can see that the additional power comes from pulling up on one pedal whilst pushing down on the other, and using my ankles to put power in for more of the rotation, but what's the equal and opposite reaction? Where's the 'fixed' point my muscles are working against? When a piston applies torque to a crankshaft, the force is coming from the expanding gases pushing down on the piston by being constrained by the cylinder and head. But on a bike, what are my muscles working against? If it still just my bodyweight, then why aren't top hill climbers heavier? Is it simply that they are also pulling up on the handlebars, or is there something else I'm missing?
Now I'm a porky old fart who cycles around for fun and errands on heavy bikes, wearing normal clothes and not even bothering with toe clips, and I realise that the key to getting up hills faster is being fastened to the pedals so you're not solely dependent on your weight pressing down on the pedals, but the more I thought about it, the more confused I got.
How do the physics of it actually work? I can see that the additional power comes from pulling up on one pedal whilst pushing down on the other, and using my ankles to put power in for more of the rotation, but what's the equal and opposite reaction? Where's the 'fixed' point my muscles are working against? When a piston applies torque to a crankshaft, the force is coming from the expanding gases pushing down on the piston by being constrained by the cylinder and head. But on a bike, what are my muscles working against? If it still just my bodyweight, then why aren't top hill climbers heavier? Is it simply that they are also pulling up on the handlebars, or is there something else I'm missing?
okgo said:
Don't overthink it. How you turn the pedals is far less important than how fit you are.
I would imagine the difference up a 5 minute climbs using flat pedals to clip pedals would be less than 30 seconds.
yeah, I get the fitness angle, it's the actual physics I'm trying to work out. I'm sitting on the saddle, I press down on the pedal by extending my thigh muscles, the pedal rotates. The bike will move forward as long as the force exerted is greater than the forces acting in the opposite direction. When the bike is on a hill, gravity (or a moment of it) becomes a more significancy force, so it needs more effort to move the bike forward up the hill. The steeper the hill, the more effort is needed.I would imagine the difference up a 5 minute climbs using flat pedals to clip pedals would be less than 30 seconds.
At some point, when the hill is really steep, it doesn't matter how strong my thigh muscles are, pressing down on the pedal will not rotate the crank, it will just lift my body off the saddle, unless I do something to prevent it. The only thing I can think of is by forcing my self onto the saddle by pulling up on the handlebars.
Somebody who is much fitter than I (and that would not be difficult) would be able to climb any hill that I can in a higher gear, but nevertheless they would surely hit this physical limit at some point?
Some Gump said:
You hit the nail on the head. On "b
d" climbs like Winnnats Pass, i can keep the pedals going in 1 of 2 ways - 1st is pull on handlebars push on pedals whilst stood, 2nd is keep sat and push more forewards than down, whilst pulling on 'tother leg.
Winnats is maybe 25% and i'm lardy (93kg). I end up stood nearly every time, because i'm going so slowly i can't balance when sat!
The bit I was climbing rises 85m in 400m, so a mere 21% grade. That is right at the limit of what's possible for me on my MTB. Even on the Pedelec it's a bit of a haul. d" climbs like Winnnats Pass, i can keep the pedals going in 1 of 2 ways - 1st is pull on handlebars push on pedals whilst stood, 2nd is keep sat and push more forewards than down, whilst pulling on 'tother leg. Winnats is maybe 25% and i'm lardy (93kg). I end up stood nearly every time, because i'm going so slowly i can't balance when sat!
Vocal Minority said:
OP - I think I can see what you are driving at, and its not necessarily about power to weight etc, you are wondering about the actual mechanical action. I am thinking about this as I go along, so please forgive me if it doesn't make sense.
I think the engine is an imperfect analogy for understanding what's going on. Whilst it is turning a crank, the power source is different. In an engine all of the power comes from the top and pushes down on an inert body (the piston). However the movement of the leg comes from the contraction and expansion of muscles along its length - and as such whilst some power comes from the bum muscle (gluteus?), an awful lot of the power comes from within the structure, rather than from an external source (such as the combustion at the top of the cylinder), therefore the need 'to push against something' and create the equal and opposite reaction.
Therefore climbers don't need to have a huge base to push against, so long as there is something - and all the power to weight stuff above becomes relevant.
That's exactly what I'm driving at, thanks! The thigh is a lever, with the fulcrum at the hip. What I was thinking about was the point that it's the rider's body that provides the resting mass for the lever to work against, and so therefore there must come a point where the force required simply lifts the body rather than moving the pedal. But as others have pointed out, the ability to gear right down means that so long as one can maintain balance, the weight of your body is always going to be sufficient to move the bike up any gradient so long as traction can be maintained.I think the engine is an imperfect analogy for understanding what's going on. Whilst it is turning a crank, the power source is different. In an engine all of the power comes from the top and pushes down on an inert body (the piston). However the movement of the leg comes from the contraction and expansion of muscles along its length - and as such whilst some power comes from the bum muscle (gluteus?), an awful lot of the power comes from within the structure, rather than from an external source (such as the combustion at the top of the cylinder), therefore the need 'to push against something' and create the equal and opposite reaction.
Therefore climbers don't need to have a huge base to push against, so long as there is something - and all the power to weight stuff above becomes relevant.
The problem I was having yesterday is that the lane I was riding up had loads of loose stones and gravel on it. If I stood on the pedals the weight came off the rear wheel and it broke traction.That and being a broken down old fart carrying far too much lard and not nearly enough muscle, of course
okgo said:
Fascinating, thanks for posting that. For the type of riding I do I want/need to be able to wear normal shoes and not worry about scratching them up with clips.Gassing Station | Pedal Powered | Top of Page | What's New | My Stuff