Why Are Recumbent Bicycles Poor Climber?

[jyl]

I've never ridden a recumbent bicycle. Everything I read says their biggest failing is in climbing. You can't stand on the pedals and pound a bigger gear, you have to downshift and spin up the hill.

What I don't understand is, why can't you pound a big gear in a recumbent, just as in a regular bicycle? I don't understand the physics.

When you stand on the pedal with a regular bicycle, suppose your leg is applying X lb of force, Y of it acts to lift your body up and X-Y acts to push the pedal. It seems that in a recumbent, your leg should be able to apply the same X, but all of it should act to push the pedal, as you have a solid backrest.

Put another way, imagine being on a leg press machine. You can press a lot more weight, braced against the backrest, than your bodyweight.

Can anyone explain the physics to me?

[Rikao4]

someone will do better..
on the bike your not really braced..
most of the weight is being lugged uphill..
instead of pushing down..

Rika

[stomachmonkey]

Torque from the crank arm.

Ever take off lug nuts by putting the lug wrench on horizontal to the ground then just step up on the end?

[tcar]

On a upright bike, when you 'pound a higher gear' you are using your body WEIGHT to lever the pedal down. Not using leg strength.

[McLovin]

that seems right to me.

It's gravity. On a regular bike, on the downstroke, you are standing on the pedal. You are putting 150 or so lbs of force on the pedal just by standing on it.

[red-beard]

John,

I expect the problem is gearing. With the backrest, you are correct in that you can put a very high force on the pedals, much higher than standing on them.

If the bike is geared for highspeed, it may not do well in hills. Also look at the crank arms. If they are short, they are setup to "spin", not for "mashing".

[wdfifteen]

Originally Posted by McLovin

that seems right to me.

It's gravity. On a regular bike, on the downstroke, you are standing on the pedal. You are putting 150 or so lbs of force on the pedal just by standing on it.

Zacky. There is no energy storage in a recumbent. The force you put on the pedal to lift yourself up on an upright is stored as potential energy, which is recovered on the way down. In the end you do the same amount of work, but you can heave yourself up on the pedal on an upright bike and rest for a fraction of a second while you ride it down. On a recumbent your muscles are working all the time. Those fractions of seconds of rest add up.

[Dantilla]

Originally Posted by McLovin

that seems right to me.

It's gravity. On a regular bike, on the downstroke, you are standing on the pedal. You are putting 150 or so lbs of force on the pedal just by standing on it.

My bike has well over 150 lbs! What a torque monster I am!

I rode a recumbent bike once. Hope I never ride another.

[dentist90]

I would think then that a recumbant might have the advantage in a short uphill sprint, where you can 'bench press' the pedals and create lots of torque...until your muscles go anaerobic.
On a conventional bike you just have to stand on the pedals and shift your weight from leg to leg: much less energy expenditure here as gravity is your friend. Plus, you could pull down on the handlebar for added torque if required, using your arm muscles as well.

[gtc]

In my experience when going up a hill with a recumbent, almost of your weight shifts from being supported by your butt/lower back to essentially fully supported by your back.
What makes climbing difficult is that you have a much more difficult time balancing. When climbing on a normal bike you are constantly yet unconsciously shifting your weight around on the pedals and handlebars to maintain balance. When you're essentially laying on your back with your hands and feet out (going up a hill on a recumbent), not only are you oriented oppositely from what you're used to, but it's also a lot harder to shift your weight around.

[gtc]

And by the way, the "weight on the pedals" argument is bunk from a physics standpoint.

[manbridge 74]

Bunk is as bunk does.

Gravity/ease of body stability wins in the end.

[wdfifteen]

Originally Posted by dentist90

I would think then that a recumbant might have the advantage in a short uphill sprint, where you can 'bench press' the pedals and create lots of torque...until your muscles go anaerobic.

You're right, on a stand-up the maximum force you can exert with one leg (the one going with gravity) is your weight. The maximum force you can exert with the upward moving leg (assuming you are attached to the pedal) is what you can pull against the handle bars. With a recumbent, you can, as you say, "bench press" both pedals until your legs give out.

[teenerted1]

have you ever seen a skinny recumbent rider?

[McLovin]

Originally Posted by gtc

And by the way, the "weight on the pedals" argument is bunk from a physics standpoint.

Would be interested in hearing why, or an explanation of the physics involved.

Also, keep in mind that a bike does not stay completely upright when going up a hill. The bike rider can tilt it side to side.

Anyways, I'm certainly open to being convinced! It seems like the bike rider can take advantage of gravity, while the recumb can't, but I'm interested in seeing why that's physically not true.

[McLovin]

I do agree that a recumb rider can probably assert more *peak* maximum torque, like described by Patrick in post 13. But a long hill climb doesn't need max peak power, it needs sustained power.

[wdfifteen]

Originally Posted by McLovin

I do agree that a recumb rider can probably assert more *peak* maximum torque, like described by Patrick in post 13. But a long hill climb doesn't need max peak power, it needs sustained power.

That's why the rest you get from "storing" energy by raising your body up on a stand-up is important. Your muscles can't get rid of lactic acid unless they relax somewhat, and you can't relax them if you are constantly pumping a recumbent. It isn't simply a matter of physics, physiology gets involved too.

[island911]

Originally Posted by wdfifteen

You're right, on a stand-up the maximum force you can exert with one leg (the one going with gravity) is your weight. The maximum force you can exert with the upward moving leg (assuming you are attached to the pedal) is what you can pull against the handle bars. With a recumbent, you can, as you say, "bench press" both pedals until your legs give out.

Actually, the pull against the handle bars is what most seem to do to add to the downward stroke/push. ...one reason that a fat down-tube (ala Cannondale) makes sense (rigidity between the bars and the crank.)

And, when going up a steep hill, the rider's load path is close to optimal for this (the fwd stance puts the bar-grip close to vertical wrt the down-stroking pedal.


...

And then there is this..

[red-beard]

You guys need to study physics

[einreb]

Not really sure what the OP means by poor climbers, but recumbents are a bit more unstable at lower speeds and mainly get a bad rap in climbing for that reason.

Random thoughts on recumbent issues on climbs:
fixed rider position
heavy bikes (generalization)
heavy riders (see above)

The geometry of the seating for a recumbent is generally built around rider comfort. The geometry of a good climbing road bike is generally built around being a good climbing road bike. yes, 'physics' comes into play... but more specifically 'human dynamics'. Standing, spreading around the pain to different muscle groups, etc is extremely beneficial to climbing.

The thought of an hour long grind sitting in some mesh backed fixed seat makes me tired just thinking about it.