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Originally Posted by Ideologue
I read that the maximum amount of torque momentarily produced by a professional (racing) cyclist is in the region of 1,000 Inch Pounds. That is 83.3r Foot Pounds, or 112.984 829 333 Newton Meters.
A 250cc motorcycle I used to ride only produced around 20 Newton Meters, so is the 112+Nm figure really an accurate one for the maximum torque a human can produce on a bicycle? It seems rather high to me. But then considering a rider with a mass of around 100kg standing up on the pedals and allowing his entire weight to push down on 175mm cranks (with a turning circle of 1099.6mm). This rider without even trying, and merely allowing gravity to pull his mass down and turning the cranks in the process, will exert approximately 539.35Nm of force through the bottom bracket spindle. What do you make of this? That's why higher RPMs are sought after in engine design. If you can double the RPM range of an engine without lowering the torque (you can't, but bear with me..., then you could gear the engine down 2:1 and get double the torque. |
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? |
Originally Posted by Ideologue
Mine was a 4-stroke (KLR 250), and it certainly did like to rev a lot (4,000 RPM = 40mph). Its maximum power output was around 21 - 27hp.
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Originally Posted by Ideologue
Hmm, I really need to study this subject some more. Can anyone recommend a decent tutorial site on torque forces, power, etc.?
http://www.v8914.com/Horsepower-v-torque.htm http://www.epi-eng.com/BAS-PwrTrq.htm http://www.team-integra.net/sections...?ArticleID=467 http://www.howstuffworks.com/question381.htm
Originally Posted by Ideologue
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?
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Note the relation between torque and crank length.
Does higher torque at the BB require a stiffer frame/BB assembly? Should big frames for big riders/long cranks be much stiffer than small frames for small riders /short cranks? Are small bikes made too stiff and big bikes too floppy ? |
Originally Posted by Mothra
It's not so much the torque, but the linear force in shear at the teeth that'll break them off. Calculate cross-sectional area of teeth at the contact point and figure breaking force at yield-strength. Divide by number of teeth and divide torque through radius of gears and see which is greater. Power is just how fast you spin the gear, so it won't hurt them that much to spin it faster... until you get into 200,000rpms+ where inertial forces starts coming into play.
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Originally Posted by Mothra
One thing to remember is your basic calculus. Power is torque integrated with respect to time. Which goes back to the gearing and RPM ideas. If you keep torque constant, but spin it twice as fast, you'll get twice the power. That's why the fastest sprinters spin such high-RPMs; there's a physiological limit to how much force & torque the human body can exert on the cranks. But if you spin it faster, you'll get more power & speed. Here's some auto sites that discuss torque & HP:
http://www.v8914.com/Horsepower-v-torque.htm http://www.epi-eng.com/BAS-PwrTrq.htm http://www.team-integra.net/sections...?ArticleID=467 http://www.howstuffworks.com/question381.htm It's not so much the torque, but the linear force in shear at the teeth that'll break them off. Calculate cross-sectional area of teeth at the contact point and figure breaking force at yield-strength. Divide by number of teeth and divide torque through radius of gears and see which is greater. Power is just how fast you spin the gear, so it won't hurt them that much to spin it faster... until you get into 200,000rpms+ where inertial forces starts coming into play. Thanks for your post and the links, they look pretty good to me! |
Originally Posted by MichaelW
Note the relation between torque and crank length.
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Originally Posted by Mothra
One of the reasons you can exert more force than your body-weight is that you'll pulling up on one side while pushing down on the other. The back-muscles is also used when pulling up on the bars to counteract the upward movement of the body. So you won't automaticaly launch yourself off the bike if you apply more than your body-weight. Of course, it takes years, decades of training in order to get the brain/muscle-coordination to spin smoothly while sprinting.
The other thing you have to consider is the gearing. It's really torque at the rear wheels that makes the bike move. Actually thrust at the contact patch is what counts. So take torque at the crank, run it through the gear-ratios, divide out radius of rear-wheel and you get linear thrust at the contact patch. You'll notice that the bike's gearing divides (reduces) the torque, while a motorcycle's gearbox multiplies (increases) the torque from the crank. Finally, it's power that's the real determination of speed. Which is torque X RPM, so the faster you spin, the more power you make. A motorcycle's torque multiplied by 9000rpms is gonna generate a heck of a lot more power than a human at 90rpms. :) You can take McEwen's 1700-watt output and work backwards through the gearing & RPMs to arrive at his torque@crank and realise the guy's a monster! My guess is that the torque numbers from the pros isn't all that much higher(and may be less) than that of the general public. But, since they can maintain high rpms all day, they have much better total power. What I think would be a real interesting experiment would be to see how a racer would perform if they carried/pulled a significant load vs someone who rides loaded as a matter of routine, or a real in-shape clydesdale(250 lb with low bodyfat). My guess(and again, it's a guess) is that as the pulled load increases, the clyde would perform better in comparison, as maximum torque becomes more important than maximum power. |
It's power that's doing the work. Torque is simply a substitue for gearing. With proper gearing, power always wins over torque.
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Power & torque are directly related through time & RPM. It's like speed vs. acceleration, there's an extra integration step with respect to time. When it comes down to it, at any given speed, 30, 60, 80kph, there's a certain amount of power required. In order to generate that power, you can use high-torque/low-RPM or low-torque/high-RPM.
Problem is you max out how much torque a human can generate since the leg muscles can only exert so much force on the crank. Then in order to get more power and more speed at 100% leg-exertion, the only thing you can do is increase RPMs once you're pushing as hard as you can. So as john bono said, the pros aren't that much stronger, but they're more coordinated and smoother so they can exert higher average torque through a wider percentage of the 360-degree pedal-stroke than us mere mortals....and do it at higher RPMs... resulting in more power & speed. :) |
Originally Posted by CdCf
It's power that's doing the work. Torque is simply a substitue for gearing. With proper gearing, power always wins over torque.
Power amplifies torque. |
Originally Posted by Ideologue
Power amplifies torque.
So it's actually the torque that is measured. If you were to measure anything on the bike, you'd measure torque at the crank or at teh rear wheel. Then combine that with a timer to measure RPMs and power is then calculated. Power is basically torque per unit time. |
That is what I meant. Poor semantics, perhaps!
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An interesting comparison of torque vs. HP comes in looking at cars while examining the weight, HP and torque. Check out performance figures between the '86 Ferrari Testarossa vs. the '86 Ferrari 288GTO... and compare to their weight, HP and torque. ;)
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The maximum moment on one crank is more than body weight. The force on that crank can be increased significantly by pulling up on the handle bar. Meanwhile the other leg can be pulling up on the other crank. I suspect that the true maximum can be somewhere in the area of twice body weight.
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Originally Posted by CTAC
His *total* power output could be 650W, but only 240W are used for *wheels motion*. He's not 100% efficient. Do you agree?
Bike designers and manufacturers have had engineers looking at the same principles and came up with something very similar to what we're all using now, which came along in the 50's. |
Originally Posted by ericgu
(Post 2764102)
Well, it's really pretty simple. Your motorcycle produced 20 NM, but it did it at 7500 RPM, while the human produced it at 75 RPM. To get 75 RPM out of the motorcycle, you'd need to gear it down 100:1, and that would multiply the torque by 100, giving you 2000 NM.
That's why higher RPMs are sought after in engine design. If you can double the RPM range of an engine without lowering the torque (you can't, but bear with me..., then you could gear the engine down 2:1 and get double the torque. The scooter engine on the other hand produces 20 N-m at lets say 1000 rpm, therefore you'll need a different gear ratio, something like 2-3, to see an rpm of 300-500 at the wheel, the torque in which case becomes 20x2=40 N-m or 20x3=60 N-m at the wheel. |
Originally Posted by MichaelW
(Post 2765113)
Note the relation between torque and crank length.
Does higher torque at the BB require a stiffer frame/BB assembly? Should big frames for big riders/long cranks be much stiffer than small frames for small riders /short cranks? Are small bikes made too stiff and big bikes too floppy ? |
Originally Posted by operator
(Post 2761576)
Sprinters are putting out what.. 2000w in the TDF sprints? Something around that neighbourhood?
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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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Y'all do know that this 'debate' had been slumbering peacefully for nearly 7 years, right?
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Originally Posted by no1mad
(Post 15808220)
Y'all do know that this 'debate' had been slumbering peacefully for nearly 7 years, right?
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Hi,
Static torque is a force like tightening a bolt. However is rotating systems it is the equivalent static force that is transferring the power in each part. A person on a bike can produce the most torque at the crank by standing on the pedals, and the most torque at the rear wheel in the lowest gear when not moving, an engine clearly can't do that at all. If you compare a motorcycle torque and power output curve at various rpm's to a human they couldn't be more different. As an engine goes faster its gets more powerful and typically has a fairly flat torque curve, though it always rises quite a lot from low revs to sensible revs. A humans torque curve drops off the faster you pedal, starting at maximum. As rpm increases it drops off slowly so power output increases, but you then hit a region where power output remains ~ constant over a range of cadences, the torque curve must be downtilted in this region, i.e. you can't pedal fast hard. rgds, sreten. . Theoretically any person can produce any arbitrary torque with a big enough lever. Anyone who is 140 lbs with 7" cranks sets off with 1000 lbs inches of torque. Producing that torque at speed in an entirely different matter. |
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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