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#11
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Maximum torque on the crank?
Crononauta wrote:
Petacchi is worth to produce a max of 130 kg during his fast sprint at Milano-Sanremo. Thanks, could be some good info. Do you know how this force was determined, and was it average or peak force? -Ron |
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#12
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Maximum torque on the crank?
On 7 Aug 2005 04:36:30 -0700, Ron Ruff wrote:
Thanks, could be some good info. Do you know how this force was determined, and was it average or peak force? Well, I don't know how scientific it is. It's what declared by Pinarello just to demonstrate strength and stiffness of its frames. Description was: "Petacchi applied to pedals a force of 130 kg each rev". Considered that Pinarello would demonstrate strength of its frames, I suppose it was the peak force. How they measured it, it wasn't explained. It could be both comparing developped speed (74 kmh - 46 mph during last 100 metres) with some measure made with telemetry during tests; or Petacchi had that device to measure power and effort, applied to crankset, like that: http://biketechreview.com/archive/po...s/image021.jpg I know that some team used it during Giro d'Italia to monitor performance of cyclers, but I don't know if Petacchi had it. -- Massimo Bacilieri AKA Crononauta Ravenna, Italy |
#13
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Maximum torque on the crank?
Per Earls61:
Could anyone tell me the maximum torque that is applied to the bottom bracket spindle of a road bicycle? Assume worst case scenarios, i.e. Very strong rider, very steep hill, etc. I would prefer a value in foot-pounds. What's the intended use of the info? ReasonForAsking: Although I don't pretend to understand the Newtonian physics/engineering stuff that greater minds will post, if you're looking for what's needed to deal with your body weight; use may be a factor. I'm about 220#, have broken one crankset - and attribute that break to extended periods of trying to learn to bunnyhop. Like I said, I don't understand the theoreticals - but there's definately a diff between somebody just lunging up a hill and the same person repeatedly trying to jump the bike - even though the weight would seem tb spread out over both cranks in the latter situation. -- PeteCresswell |
#14
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Maximum torque on the crank?
Werehatrack wrote:
On 6 Aug 2005 19:25:10 -0700, "Earls61" wrote: Could anyone tell me the maximum torque that is applied to the bottom bracket spindle of a road bicycle? Assume worst case scenarios, i.e. Very strong rider, very steep hill, etc. I would prefer a value in foot-pounds. Max-torque on the spindle would probably be achieved when doing a "trackstand" with the cranks nearly horizontal, in which the rider's weight is applied about equally to both pedals. Given a crank of 175mm in length and a rider weight of 350 lbs (not common, but certainly within the realm of what exists), I get 200 ft/lbs of torque applied to the spindle. the force and moment arm are multiplied so the unit is ft-lb, not ft/lb. Clearly this is wrong. With equal opposing torque on the ends of the spindle, it carries only 100 ft-lb applied at each pedal. Any "weight" applied to the left crank (put it forward) that had been applied to the right in your example would increase the spindle torque. I doubt that this would be exceeded when pedalling in most cases, though it might on hard climbs if the rider is both standing and applying additional force by pulling up on the bars. The difference is probably small, however...and with the exception of one of the more heroically-sized denizens of this group, I would not expect to find a 350lb rider trying that tactic very often. Whenever standing, when the left pedal is forward the 350 pounder would get about 200ft-lb. There is a small reduction due to the downward acceleration of the foot & leg minimized by a steep gear. Pulling up on the bars or lifting the right (rearward) pedal increases the number attainable without accelerating the body upward. The OP said maximum so I'll get ridiculous: A big guy jumps off his seat onto a forward pedal on the front of a tandem when there's somebody really big on the back seat so the tire doesn't slip. If nothing breaks, the spindle torque is limited by the force which the jumper can produce in his "landing" leg. 1000 lb two legged squats are possible so over 500 lb from one leg ought to be doable briefly. Lets put it on a 200mm crank instead of wimpy 170s like I use. about 350 ft-lb! |
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Maximum torque on the crank?
On 6 Aug 2005 19:25:10 -0700, "Earls61"
wrote: Could anyone tell me the maximum torque that is applied to the bottom bracket spindle of a road bicycle? Assume worst case scenarios, i.e. Very strong rider, very steep hill, etc. I would prefer a value in foot-pounds. Thanks, Bob Dear Bob, Various posts in this thread have mentioned "flinging" and "jumping" and similar notions in connection with the rider's weight. The only time that this occurs normally is when the rider stands up. If the rider exerts more force than his body weight on the pedal with one leg, his body rises. To see what would really happen, try this abnormal maneuver: While already standing up to pedal, start coasting and rise up further by putting the pedals horizontal and straightening both legs. This weird and awkward posture does indeed raise your center of mass (your hips are higher), so it allows you to drop your weight down on the pedal, but only once and with no more force than you exerted when you raised yourself up. When we speak of "throwing" our weight on the pedal, it's pretty much wishful thinking. We really just lean from side to side to move our center of mass over the pedal and push down. Unless you see a rider's hips rising and falling, he's just shifting his weight back and forth as he pushes down with alternate legs, not throwing his weight up or down. During normal riding (meaning something sustainable for more than a single downstroke), the hips stay at about the same distance from the bottom bracket, neither rising nor falling, with one leg straightening and extending, while the other leg bends and retracts. Our center of mass doesn't "jump" up and down even as much as it does when we walk or run. Carl Fogel |
#16
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Maximum torque on the crank?
Alfred Ryder writes:
Could anyone tell me the maximum torque that is applied to the bottom bracket spindle of a road bicycle? Assume worst case scenarios, i.e. Very strong rider, very steep hill, etc. I would prefer a value in foot-pounds. That is so simple that I might take a shot at it. The left pedal is the only one that puts torque on the spindle. The right pedal cannot put torque on the spindle. The crank arm is usually right at 7 inches long. Very rarely is a rider going to put more than 200 pounds of force on a single pedal. However, if the rider weighs, say, 300 pounds and then bounces on the pedal while the crank arm is parallel to the ground, he might get 350 pounds on it. Thus 350*7/12 is about 200 foot pounds. And the more reasonable rider does 200*7/12=117 foot pounds. It probably does not matter much how strong the rider is or how steep the hill is. I have ridden up the 31.5% grade of Filbert St in SF in a 47-21 ratio. At a combined weight of rider and bicycle of a little over 200lbs that gives about 326lbs to hold the bicycle at a stand still. Not a lot of that came from pulling up on the other pedal, this being done with worn metal cleats and foot straps. I also id this in the rain, showing that traction on wet concrete is not a problem although the roughness of the hand towelled surface is. Further, if the chain is in a relatively small chain ring, say one with a radius of 2 1/2 inches, the force on the chain from the above heavy rider is 200*12/2.5 which is about 960 pounds. Of course gradients and pedal force are all related by the chain ratio and wheel diameter but that was not the question here. Jobst Brandt |
#17
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Maximum torque on the crank?
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#18
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Maximum torque on the crank?
Crononauta wrote:
On 7 Aug 2005 04:36:30 -0700, Ron Ruff wrote: Thanks, could be some good info. Do you know how this force was determined, and was it average or peak force? Well, I don't know how scientific it is. It's what declared by Pinarello just to demonstrate strength and stiffness of its frames. Description was: "Petacchi applied to pedals a force of 130 kg each rev". If it was an average force, we'd have 130kg x 9.81m/s^2 x 3.14 x 2 x ..175m x 120?rpm x 1/60 min/sec = 2,803W... which I think is more power than he could sustain in a sprint... so it probably is a peak value. The cadence I'm not sure of; it would likely be higher than 120 unless it was uphill. What can a good sprinter put out these days? Isn't it around 1,500W? Just for fun, lets put him on a steep hill with a starting cadence of 60rpm instead of 120rpm. Would he be able to produce the same power? The technique would be a little different, but I'd wager that he could get close... and the ratio of peak force to average force would be at least as great. To do that he'd have to double the peak pedal force to 260kg (572lbs). -Ron |
#19
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Maximum torque on the crank?
On 7 Aug 2005 14:05:24 -0700, "Ron Ruff"
wrote: wrote: When we speak of "throwing" our weight on the pedal, it's pretty much wishful thinking. We really just lean from side to side to move our center of mass over the pedal and push down. Unless you see a rider's hips rising and falling, he's just shifting his weight back and forth as he pushes down with alternate legs, not throwing his weight up or down. I agree, if we are just looking at what a person "normally" does when they ride out of the saddle at a relatively easy pace... but I think the OP is interested in the worst case scenerio. If you perform an uphill sprint; a "violent" all-out effort for a few seconds... particularly if you start in a fairly tall gear... it's easy to get a force much greater than your weight during the power stroke. The hips don't need to rise and fall very much... even if you completely unweight your forward leg, and "punch" down with all your might. [snip] Dear Ron, Sorry, but I'm not following you. When you say "completely unweight your forward leg" . . . Where is the pedal? (Let's say noon is straight up, 3 o'clock is toward the rear axle, 6 o'clock is straight down, and 9 o'clock is toward the front axle.) What is the leg's bend? (Let's try straight, half-bent, full-bent.) Where did your weight shift to? (Other leg? Hurled upward into the air?) Carl Fogel |
#20
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Maximum torque on the crank?
On Sun, 07 Aug 2005 17:01:47 -0700, "(PeteCresswell)"
wrote: Per : Various posts in this thread have mentioned "flinging" and "jumping" and similar notions in connection with the rider's weight. The only time that this occurs normally is when the rider stands up. Or bunny hops or lands from a drop. Dear Pete, I like your kangaroo-like point, even though I was thinking of steadily repeatable pedal motion. But if we think of the original poster's question about maxium torque on the crank spindle . . . There's no torque on the spindle on landing if the crank is vertical. And there's no net torque on the spindle on landing if the crank isn't vertical, assuming that the rider's weight is distributed evenly on the two pedals. Carl Fogel |
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