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  #1  
Old 07-14-2011, 04:01 PM
Oldguyonabike Oldguyonabike is offline
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Default Physics question

I have a physics question that's been nagging me for awhile.
Why is it that we balance better up and out of the saddle (standing) when doing so raises our center of gravity which, technically, should be less steady?
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Old 07-14-2011, 04:14 PM
Psyfalcon Psyfalcon is offline
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When you're sitting on a saddle, you have a limited ability to move your weight around. Standing, you don't have that constraint.
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Old 07-14-2011, 09:21 PM
Alan Alan is offline
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When I rode my first recumbent it felt sort of tippy despite the center of gravity being way low. The rep explained to me that it was sort of like how it's easier to balance a broom on your fingertip than a lighter, shorter column like a straw (the 'bent being like the straw). I suppose that's something to do with "equal and opposite reaction."

What Psyfalcon says is true, too. I watched Ryan Leech at Pedal Nation as he rode his bike on top of a 4" diameter tube, about 6 feet off the ground. Not only was his butt off the saddle but one leg was off the pedals, waving around for balance, most of the time.
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Old 07-15-2011, 09:26 AM
Oldguyonabike Oldguyonabike is offline
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Makes sense. Its not just the height; its the distribution.

I'm helping a 50+ woman co-worker who is starting to ride and who brought it up because she's running out of gears going uphill and nervous about the whole "standing up thing". I really hadn't noticed how much time I spend up and out of the saddle (slowing to a stop, stretching my calves, accelerating, hills, ....) until she brought it up. When she said she felt unsteady standing up I countered with that's what I do to GET steady. But I couldn't explain why.

Thanks! Enjoy the weekend!
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Old 07-15-2011, 10:59 AM
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wsbob wsbob is offline
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Quote:
Originally Posted by Oldguyonabike View Post
Makes sense. Its not just the height; its the distribution.

I'm helping a 50+ woman co-worker who is starting to ride and who brought it up because she's running out of gears going uphill and nervous about the whole "standing up thing". I really hadn't noticed how much time I spend up and out of the saddle (slowing to a stop, stretching my calves, accelerating, hills, ....) until she brought it up. When she said she felt unsteady standing up I countered with that's what I do to GET steady. But I couldn't explain why.

Thanks! Enjoy the weekend!
Arm, hand and chest strength also factors into sense of stability when standing up and pedaling. Unless Oldguy's friend has been getting some other kind of workout that would strengthen those muscle areas, she's possibly not going to feel very steady when getting up on the pedals. This was on my mind earlier, but I've been reading and thinking about people's answers. Actually, foot/ankle strength too. I remember there being a danger with plain, flat rubber pedals on my old Schwinn cruiser allowing my feet to slip off in a mad power acceleration, if I wasn't careful.

When standing on the pedals, it can take a while to get a sense of how to manipulate body mass so as to direct the power of its weight onto the pedals and into the cranks while still being in balance on the bike. Most people wouldn't consciously think about what's going on here. Why should they? It's something people do rather instinctively, as they do when learning to balance themselves on a bike in the first place. It's kind of nice though, for this gal to have a thoughtful person like oldguy, giving her support and encouragement!

Last edited by wsbob; 07-15-2011 at 09:24 PM.
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Old 07-15-2011, 12:32 PM
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dmc dmc is offline
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It's the same concept as taking a manikin with the realistic weight of a human and seeing if you can get it to stand upright on its feet as a base. There are lots of muscle movements in our feet/legs alone that are constantly going off and on to keep our body balanced at any given time. Not to mention the rest of the muscles in the body.
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Old 07-16-2011, 12:10 PM
tonyt tonyt is offline
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Hey Alan,

The obsession with low center of gravity in cycling is a great example of people taking for granted that a particular premise (lower center of gravity is better) is true.

I could go on and on, but a brief example should suffice.

Which is easier to balance on its end, a long handled broom or a short handled broom? A short handled broom is more difficult because you have to make more and faster corrections. I think this is a lot like the difference between balancing on a regular bike and a short recumbent.

Last edited by tonyt; 07-16-2011 at 12:10 PM. Reason: clarity
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Old 07-18-2011, 03:30 PM
Oldguyonabike Oldguyonabike is offline
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So, this morning I was nearly to work and came up out of the saddle to get over a little rise and the right egg-beater fell out and the force of the down stroke without a peddle underneath threw me to the ground. A little road rash to the elbow and hip but otherwise OK. I was on the 205 bike path so there wasn't any traffic. Once again, glad I wear a helmet because my head hit hard. If I'd been seated I would have recovered enough balance to not have taken the dive.

So, maybe this is off subject. Yeah, its off subject, but anyway...

How would the right pedal come unscrewed from the crank? They are machined to tighten with the rotation of the pedal. That's why the left is counter sunk. It didn't shear off. I was able to screw it back in. Weird.
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Old 07-18-2011, 04:03 PM
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Dovestrobe Dovestrobe is offline
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Quote:
Originally Posted by Oldguyonabike View Post
How would the right pedal come unscrewed from the crank? They are machined to tighten with the rotation of the pedal. That's why the left is counter sunk. It didn't shear off. I was able to screw it back in. Weird.
Perhaps you disengaged unconsciously by turning your heal prior to riding vertical on your pedals or you were not fully engaged to begin with. Get a marriage license!
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Last edited by Dovestrobe; 07-18-2011 at 04:05 PM.
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  #10  
Old 07-22-2011, 01:36 PM
tonyt tonyt is offline
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Default "counter sunk" has nothing to do with it

Quote:
Originally Posted by Oldguyonabike View Post
How would the right pedal come unscrewed from the crank? They are machined to tighten with the rotation of the pedal. That's why the left is counter sunk. It didn't shear off. I was able to screw it back in. Weird.
The left pedal is simply a left-hand thread (turn left to tighten). There isn't any counter-sinking going on at all.

My guess is that your bearings are going. When your bearings in good shape, they act to tighten the pedal, when they go bad and begin to drag, they act to unthread the pedal. Egg-beaters are notorious for short bearing life.
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