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Originally Posted by CdCf
(Post 2761710)
Because it takes POWER to go fast, and power is force multiplied by speed, or in this case pedal torque multiplied by rotational rate (cadence). If your torque is indeed higher throughout (which I doubt), his cadence at the lower torque level he is at, is sufficiently greater than your speed.
Let's say a sprint finish for Robbie McEwen requires him to put out 500 W. His gear is 53/11 and he's riding on 20 mm tyres. Let's also assume that the sprint is at 60 km/h. 60 km/h is 16.7 m/s, and the circumference of a wheel is 2.074 m. That means ~8 wheel revolutions per second, and the 4.82 pedal-to-wheel ratio gives us a cadence of ~100, or 1.7 revs/sec. Dividing power by "second-cadence" gives torque, and 500 W / 1.7 r/s = 294 Nm. That's his average torque. Peak torque per half pedal cycle will be higher. How much higher is hard to say. This was just an example. His actual speed and power during a sprint may well be higher. But you still calculate it the same way. |
Originally Posted by rydabent
(Post 15817020)
This is an interesting thread. Some posters touched on what I question. On a DF if a rider is standing and his or her full weight is on one pedal, some of the numbers quoted seem low. Now if a 200 pound rider is pushing down his weight, plus the force added by pulling up on the handle bars for maybe 90 degrees the torque would seem to me would be around 250 foot pounds. That would be repeated with the other leg, for a total of 180 degrees. Then divide that by 2, because of a full 360 degree circle. Then drop that by the gearing of say 42 by 15 and you would get the torque actually applied to the ground. So to me you would have 125 times .3 would equal 37.5 foot pound of torque. Those are approx numbers for a 200 pound person and would be reduced by less weight and less pulling up on the handle bars. That would seem to me to be the max, but again that would be reduced by mechanical efficiencies. It also occurs that that would be the torque on the cassette. It would again have to be reduced by the relationship of the sprocket to the wheel depending on the size. I believe that is why my Tailwind bent would take off like a scalded rabbit with its 20 inch rear wheel. Comments?
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Originally Posted by Ideologue
(Post 2764675)
Hmm, I really need to study this subject some more. Can anyone recommend a decent tutorial site on torque forces, power, etc.?
The interesting question is: Cog and sprocket design? I thought that these components are rated for torque, not power. I wonder what the maximum torque rating is for various bicycle sprocket sizes? |
Power or horsepower that everyone talks about is basically torque over a period of time. Torque is the thing that actually moves bikes, cars etc. Thats why trucks are tuned for max torque rather than max horsepower.
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I'm thinking Match sprint Track racers like Scottish multi world championship,
Olympic Multi Gold Medalist Chris Hoy, [Recently retired], were, able to put out more torque on the cranks than the road guys doing 100 miles in a road stage before the field sprint for the finish line. |
Originally Posted by rydabent
(Post 15826391)
Power or horsepower that everyone talks about is basically torque over a period of time. Torque is the thing that actually moves bikes, cars etc. Thats why trucks are tuned for max torque rather than max horsepower.
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Oodles of torque at the rear wheel, if the gear ratio is low enough..
like a wrench with a really long cheater pipe stuck on the end. |
Originally Posted by kenji666
(Post 15808108)
You can't compare pedaling a bicycle to doing 400 lb leg presses, since you're not pushing against a padded steel frame. The only reaction force that allows you to push against the cranks is the force produced by your arms pulling against the handlebars plus your body weight. Most do not have the upper body strength to pull up with that much force.
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Yes yes this thread is like a century old, but I have recently become obsessed with Torque during cycling.
Does anyone know if they can make their Garmin or any head unit display Torque (Nm) recorded by their power meter? I have managed to display it but only in the calibration screen, not during rides. I can see my Torque numbers post-ride. Does anyone know what sort of torque measuring limits are set on power meters (for example 250Nm). As I have see many are limited to 2000w and have a rpm range of 30-200, so surely there should also be a Torque limit? |
Originally Posted by CTAC
(Post 2761395)
Muscle works like a spring. It pushes pedal down and pushes body up. Have you heard about Newton laws? If force is greater than the body weight you are just bouncing up. Yes, you can compensate for that with your arm holding handlebars tight, but not by much.
As for the Robbie, he is faster *average* moment is greater then yours, not maximum. For your comment about Newton, presumably you are referring to his 3rd law, in which case, if the sum of the forces applied is greater than weight, the pedal then pushes the rider in the opposite direction in which the rider pushes the pedals in such a manner that the rider rises if the transfer of that energy is not inelastic. |
Looking at it very simply, a 175 pound rider using a 175 mm crank arm could push down at about 60% of his weight in foot pounds. That figures out to approx 100 foot pounds. That would occur when the pedal is at 90 degrees. You have to understand that if pedaling torque is plotted it would be in a saw tooth. So you have to state if you are taking maximum torque or ave torque.
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do fig newtons count?
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Don't forget about the other leg pulling up.
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All I know is I snapped a pedal off a few months ago.
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Originally Posted by CTAC
(Post 2761127)
Torque is force times radius. Assuming crank length 175mm and rider's weight of 140 pounds, that gives us 80ft.lb or 109 NM torque when rider is standing and crank is *parallel to the ground*. The average torque will be much lower, something about 50NM.
I am student working on a pedel assist bicycle project. You have mentioned that average torque a human can aply ia approx. 50 NM. Can u please share some written or published document where it is mentioned. I want to know the minimum force a human can apply so that motor will assist the remaining. Thanks. :) |
Don't forget how often the different 'engines' rotate here either. We're talking a human-powered, 100 RPM machine vs a 2000, 3000, 4000, (+++) RPM engine on the bike right?
So if I put out 500 lb-ft per spin and spin 100 times a minute (probably actually high for a heavy push), but a motorcycle engine puts out 200 lb-ft per spin but spins 8,000 times per minute, I have a feeling the motorcycle wins the race. |
Must be a good zombie thread...eleven years old, resurrected three or four times.
...motorcycle is 500+ pounds, human is 165, but motorcycle would still win. |
Is Peter Tork of the Monkees involved in this somehow?
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Originally Posted by JanMM
(Post 19657542)
Is Peter Tork of the Monkees involved in this somehow?
Or maybe Tomás de Torquemada? I mean a 4 time Zombie Thread has to be a sin of some kind... |
My two cents here. Yes not only does the cyclist on a DF bike push down on the crank with his weight, but if standing he has extra push by pulling up on the handle bars. If he does not pull up, he can only push down by the amount of his weight.
Then there are the bent riders like myself. Depending on the design of of a bent or trike, the bent rider can use their leg strength to create torque plus being able to wedge himself between the pedal and the back of the seat. |
Originally Posted by rydabent
(Post 19658809)
My two cents here. Yes not only does the cyclist on a DF bike push down on the crank with his weight, but if standing he has extra push by pulling up on the handle bars. If he does not pull up, he can only push down by the amount of his weight.
Add in clipless pedals, and get out of the saddle, and the physics get way more interesting. Take a look at the upper body mechanics going on in the Chris Hoy video in post #58. Wow. I'd love to put a strain gage on the stem of that rig. Heck, he's not even in the saddle untill the end of the back straight. |
Maximum human torque? Ask Archimedes.
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No body mentioned that a sprinting cyclist (especially track sprinters) is pushing down on one pedal while pulling up on the opposite pedal; plus the sprinter is also pulling up on his bars.
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Torque
When I am standing and cranking up a steep rise my weight is not constant. Try bouncing up and pushing down on a foot scale. I am pushing down on the pedal with the momentum of my falling 225 pounds plus all the push I can muster. This must be a whopping amount because it becomes very difficult very quickly. I then morph into an air machine to try not to die before reaching the top. Now I’m on a single speed so my cadence can’t drop below a certain level or my pedals will break. Or crank. Or chain. Or B.B. done it all...a high cadence seems to get those pedals over the arc.
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4 time zombie thread...
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