|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
Elliptical Chainrings
"none (Yannick Tremblay)" yatremblay@bel1lin202. wrote in message
... In article , Steve Freides wrote: Mower Man wrote: Isn't it the point that elliptical chain rings actually vary the gear ratio? Forget the number of teeth, they're only there 'cos a chain is used. Think of diameter. Variable diameter. Honest. Think drive belt? Big pulley vs small pulley? But big pulley versus small pulley, first of all, means something different for belt drive than for one with teeth. If one pedal revolution gets you 39 teeth spaced evenly apart, what's the difference what the shape is? For a belt driven system, a change in shape could at least mean a change in circumference. For 1 complete revolution, there is no difference. Absolutely correct. However what about 1/4 of a revolution or 1/8 of a revolution? Then the diameter of the "big pulley" does differs. True, but *overall* diameter doesn't change as the number of teeth remains the same. So, the gear ratio remains the same. And, as long as the chainring radius is no greater than that of the crank arm there isn't even any leverage difference as if often the (erroneous) claim, due to the fact that it's the length of the crank arms that determines the lever arm. -- Sir Gregory |
Ads |
#12
|
|||
|
|||
Elliptical Chainrings
"Friso" wrote in message
... Yannick Tremblay yatremblay@bel1lin202.(none) wrote: In article , Steve Freides wrote: Mower Man wrote: Isn't it the point that elliptical chain rings actually vary the gear ratio? Forget the number of teeth, they're only there 'cos a chain is used. Think of diameter. Variable diameter. Honest. Think drive belt? Big pulley vs small pulley? But big pulley versus small pulley, first of all, means something different for belt drive than for one with teeth. If one pedal revolution gets you 39 teeth spaced evenly apart, what's the difference what the shape is? For a belt driven system, a change in shape could at least mean a change in circumference. For 1 complete revolution, there is no difference. Absolutely correct. However what about 1/4 of a revolution or 1/8 of a revolution? Then the diameter of the "big pulley" does differs. I think that's the point of Biopace and this new system (has it got a name yet?). The strength needed to rotate 1 cycle is equal, but with an elliptical chainring this strength is supposed to be more equally distributed. Given the way everything is shaking and non-smooth there must be an effect. I would think this effect is negative, also given the silent passing of Biopace, but given the performance of Froome that doesn't make sense. I wonder: is it still possible to stand up on your pedals when you're going uphill, or is this why Froome is almost always sitting? Froome mostly sits because any energy used moving the body up and down when standing is energy wasted compared to not lifting the body and staying seated. A bicycle is a machine which should be used for best mechanical advantage. Standing and running on the machine as opposed to being seated on the machine and spinning both pushing and pulling causes the machine to become more efficient. Lifting the pedals while seated causes more total energy to be put into the machine than lifting when standing which mostly works against the inertia of the body mass thus moving the body up and down with the push-pull and this disrupts the smooth turning of circles which is more efficient than some jerky motion. Froome seems to have this insight. Then there's the factor of wind resistance. Every pro should know that standing causes more wind resistance. Why stand when it's going to cost you watts and wear you out prematurely? It's high time pro cyclists started relying less on drugs and more on using their heads. -- Sir Gregory |
#13
|
|||
|
|||
Elliptical Chainrings
"Steve Freides" wrote in message
... [trim] You misread what I wrote. I don't assume that a change in circumference matters, either - you could accomplish the same thing with a larger or smaller, but still round, pulley. The reason tests cannot confirm that this idea works is simple - it doesn't. Neither the rear wheel nor your legs care about the shape of the chainring. When you're pulling one tooth's worth of chain, that's what you're doing, period! BINGO!!! |
#14
|
|||
|
|||
Elliptical Chainrings
In article ,
Friso wrote: Yannick Tremblay yatremblay@bel1lin202.(none) wrote: In article , Steve Freides wrote: Mower Man wrote: Isn't it the point that elliptical chain rings actually vary the gear ratio? Forget the number of teeth, they're only there 'cos a chain is used. Think of diameter. Variable diameter. Honest. Think drive belt? Big pulley vs small pulley? But big pulley versus small pulley, first of all, means something different for belt drive than for one with teeth. If one pedal revolution gets you 39 teeth spaced evenly apart, what's the difference what the shape is? For a belt driven system, a change in shape could at least mean a change in circumference. For 1 complete revolution, there is no difference. Absolutely correct. However what about 1/4 of a revolution or 1/8 of a revolution? Then the diameter of the "big pulley" does differs. I think that's the point of Biopace and this new system (has it got a name yet?). The strength needed to rotate 1 cycle is equal, but with an elliptical chainring this strength is supposed to be more equally distributed. The key is that the human ability to deliver power and generate torque varies depending on the position of the pedals. If you had a human with perfect spinning pedalling movement able to generate the same amount of torque at every points over 360 degs then these system would be useless. But they are an attempt to compensate for the imperfect human engine (and pedals). Given the way everything is shaking and non-smooth there must be an effect. I would think this effect is negative, also given the silent passing of Biopace, but given the performance of Froome that doesn't make sense. Why would you think that they have a negative effect? Shimano, Rotors, and the like have made scientific studies on the subject. We could dismiss some of it as marketing gimmick, other as flawed science but I would not dismiss the Sky team and David Brailsford. The UK cycling team has achieved so much success in the Olympics and WC in large part by preparing and training better, harder and more scientifically than anyone else. Team Sky is most probably the most scientifically trained and tested team. I would be incredibly surprised if Chris Froome has not spent hundreds of hours on a training bikes in the lab trying different setup including circular chain rig and ovoid chain rig. The difference may have been only 0.5% or even less but Brailsford believes in summing all these small minor advantages and making it a winning difference. I wouldn't even be surprised that the exact angle of the ovoid for Froome differs between his mountain climbing bike and his time trial bike and that they all differ from Wiggins ones all of that based on labs measurement for the specific athlete under specific conditions. Brailsford and his team are that anal with regards to details. In act, the above probably highlight one of the problem with Biopace in that it was one setup that may have been good for a certain type of rider with a certain pedalling style but not for a different rider with a different pedalling style. I wonder: is it still possible to stand up on your pedals when you're going uphill, or is this why Froome is almost always sitting? Hmm, not sure. In theory "dancing on a bike" is not very good and a waste of effort in the long term although climbers like to do it for short efforts. I don't seem to recall someone like Indurain standing up too often either. I'd put it down to riding style. Yani |
#15
|
|||
|
|||
Elliptical Chainrings
" Sir Gregory Hall, Esq·" åke wrote in message
... "Friso" wrote in message ... Yannick Tremblay yatremblay@bel1lin202.(none) wrote: In article , Steve Freides wrote: Mower Man wrote: Isn't it the point that elliptical chain rings actually vary the gear ratio? Forget the number of teeth, they're only there 'cos a chain is used. Think of diameter. Variable diameter. Honest. Think drive belt? Big pulley vs small pulley? But big pulley versus small pulley, first of all, means something different for belt drive than for one with teeth. If one pedal revolution gets you 39 teeth spaced evenly apart, what's the difference what the shape is? For a belt driven system, a change in shape could at least mean a change in circumference. For 1 complete revolution, there is no difference. Absolutely correct. However what about 1/4 of a revolution or 1/8 of a revolution? Then the diameter of the "big pulley" does differs. I think that's the point of Biopace and this new system (has it got a name yet?). The strength needed to rotate 1 cycle is equal, but with an elliptical chainring this strength is supposed to be more equally distributed. Given the way everything is shaking and non-smooth there must be an effect. I would think this effect is negative, also given the silent passing of Biopace, but given the performance of Froome that doesn't make sense. I wonder: is it still possible to stand up on your pedals when you're going uphill, or is this why Froome is almost always sitting? Froome mostly sits because any energy used moving the body up and down when standing is energy wasted compared to not lifting the body and staying seated. A bicycle is a machine which should be used for best mechanical advantage. Standing and running on the machine as opposed to being seated on the machine and spinning both pushing and pulling causes the machine to become (correction) LESS efficient. Lifting the pedals while seated causes more total energy to be put into the machine than lifting when standing which mostly works against the inertia of the body mass thus moving the body up and down with the push-pull and this disrupts the smooth turning of circles which is more efficient than some jerky motion. Froome seems to have this insight. Then there's the factor of wind resistance. Every pro should know that standing causes more wind resistance. Why stand when it's going to cost you watts and wear you out prematurely? It's high time pro cyclists started relying less on drugs and more on using their heads. -- Sir Gregory |
#16
|
|||
|
|||
Elliptical Chainrings
In article ,
Steve Freides wrote: none (Yannick Tremblay) wrote: In article , Steve Freides wrote: Mower Man wrote: Isn't it the point that elliptical chain rings actually vary the gear ratio? Forget the number of teeth, they're only there 'cos a chain is used. Think of diameter. Variable diameter. Honest. Think drive belt? Big pulley vs small pulley? But big pulley versus small pulley, first of all, means something different for belt drive than for one with teeth. If one pedal revolution gets you 39 teeth spaced evenly apart, what's the difference what the shape is? For a belt driven system, a change in shape could at least mean a change in circumference. For 1 complete revolution, there is no difference. Absolutely correct. However what about 1/4 of a revolution or 1/8 of a revolution? Then the diameter of the "big pulley" does differs. Yan You misread what I wrote. I don't assume that a change in circumference matters, either - you could accomplish the same thing with a larger or smaller, but still round, pulley. The reason tests cannot confirm that this idea works is simple - it doesn't. Neither the rear wheel nor your legs care about the shape of the chainring. When you're pulling one tooth's worth of chain, that's what you're doing, period. "When you're pulling one tooth's worth of chain" Yes absolutely, for the *rear* cog. But how many degree of rotation of the pedals are needed to move 1 tooth at the back? On a circular chain rig, pulling 1 tooth of the front 36 rig will pull 1 teeth of the rear 18 cog. This occurs on a 10 degree rotation of the pedals regardless of the pedal position and causes a 20 degree rotation of the rear wheel. On an ovoid chain rig however, this is not the case. While the ovoid rotate 10 degree, its active diameter also changes. The change in active diameter of the front can be observed by looking at the derailler moving in an out as the front rig rotates. It is kind of equivalent to the front rig dynamically changing between, say 35 and 37 teeth during a full rotation. (This is possible because only about half of the front rig is touching the chain at any point in time and there is slack in the chain). For some section of the rotation the chain is being pulled by the rotation and is getting pulled also by the increase in diameter while for other sections, the chain will be pulled by the rotation but some of this will be cancelled by the reduction in diameter. So while 360 deg front = 720 degs rear, for some part of the rotation, 10 degree front could result in 19.5 or 20.5 degs rear (because the chain is also being pulled by the increase in diameter) rather than a constant 20 degree. There is a difference and this difference can be measured. The mechanics of ovoid/biopace/etc are pretty easy to demonstrate experimentally or prove mathematically. What is a lot less clear are the real benefits to the cyclists. Yan |
#17
|
|||
|
|||
Elliptical Chainrings
In article ,
Sir Gregory Hall, Esq· åke wrote: "none (Yannick Tremblay)" yatremblay@bel1lin202. wrote in message ... In article , Steve Freides wrote: Mower Man wrote: Isn't it the point that elliptical chain rings actually vary the gear ratio? Forget the number of teeth, they're only there 'cos a chain is used. Think of diameter. Variable diameter. Honest. Think drive belt? Big pulley vs small pulley? But big pulley versus small pulley, first of all, means something different for belt drive than for one with teeth. If one pedal revolution gets you 39 teeth spaced evenly apart, what's the difference what the shape is? For a belt driven system, a change in shape could at least mean a change in circumference. For 1 complete revolution, there is no difference. Absolutely correct. However what about 1/4 of a revolution or 1/8 of a revolution? Then the diameter of the "big pulley" does differs. True, but *overall* diameter doesn't change as the number of teeth remains the same. So, the gear ratio remains the same. And, as long as the chainring radius is no greater than that of the crank arm there isn't even any leverage difference as if often the (erroneous) claim, due to the fact that it's the length of the crank arms that determines the lever arm. Please, this is pure mathematics and mechanics. The "active" "current" diameter of the front rig changes dynamically during a rotation which means that the current amount of rotation of the pedal that is needs to achieve some specific rotation of the rear wheel with the pedal-crank-rig-chain-cog-wheel assembly changes dynamically. In average over 360 degree it is the same but instantaneously it differs. The problem and complexity occurs when you start introducing a bloody human in the equation and these pesky things are pretty much impossible to model mathematically and are notoriously irregular between individuals. Serously, by all mean disagree that it has any benefits to humans (I am certainly not convinced either) but lets not disagree on mathematics. Yan |
#18
|
|||
|
|||
Elliptical Chainrings
"none (Yannick Tremblay)" yatremblay@bel1lin202. wrote in
message ... On an ovoid chain rig however, this is not the case. While the ovoid rotate 10 degree, its active diameter also changes. Active diameter doesn't matter. Only the gear ratio matters and that gear ration depends on number of teeth. The change in active diameter of the front can be observed by looking at the derailler moving in an out as the front rig rotates. It is kind of equivalent to the front rig dynamically changing between, say 35 and 37 teeth during a full rotation. (This is possible because only about half of the front rig is touching the chain at any point in time and there is slack in the chain). Wrong! The gear ration doesn't change. Only the slack in the chain changes depending upon the position of the shape of the chainring. The derailleur pulleys are a chain tensioner so of course when the chain becomes slack it takes up the slack. This doesn't mean the gear ratio is changing. One could use a square or rectangular chainring but if it had 53 teeth then the shape of it won't change the gear ratio. It is gear ratio that determines mechanical advantage not gear shape. Oddly shaped gears only result in reduced efficiency compared to circular gears. -- Sir Gregory |
#19
|
|||
|
|||
Elliptical Chainrings
On 18/07/2013 11:04 PM, Steve Freides wrote:
Mower Man wrote: On 18/07/2013 9:26 PM, Steve Freides wrote: Davey Crockett wrote: " Sir Gregory Hall, Esq·" a écrit profondement: Elliptical chainrings are a GIMMICK. Why? Because gearing depends upon the number of teeth on the chainring and the number of teeth on the cassette. When spinning the crankshaft it doesn't matter one iota what shape the chainring is. All that matters is the relationship between the number of teeth on the chainring and the number of teeth on the particular cassette ring. Any idiot who thinks otherwise is just that, an idiot! The original concept, way back, was that the eliptical shape allowed one to transmit the same, or reasoably the same, power to the drive train whether the cranks were at TDC, BDC or any other aspect. (TDC=Top Dead Center) Wouldn't it make more sense, then for the pedaling circle to be elliptical, rather than the chainrings? I'm not quite sure how one would achieve that end, but Sir Gregory Hall seems to have a point here - if you're still pedaling circles, it doesn't matter how the chainrings are shaped. Davey remembers Jeff Bernard proudly sporting the "BioPace" decal on his regular (round) chainring. He didn't believe the Shimano BS either apparently. Ah, yes, I did try BioPace back in the day. NB: they, nor any other non-round chainrings, are terribly useful on a fixed gear. -S- Isn't it the point that elliptical chain rings actually vary the gear ratio? Forget the number of teeth, they're only there 'cos a chain is used. Think of diameter. Variable diameter. Honest. Think drive belt? Big pulley vs small pulley? But big pulley versus small pulley, first of all, means something different for belt drive than for one with teeth. If one pedal revolution gets you 39 teeth spaced evenly apart, what's the difference what the shape is? For a belt driven system, a change in shape could at least mean a change in circumference. -S- See next post - totally correct! -- Chris 'Fashion is a form of ugliness so intolerable that we have to alter it every six months.' (Oscar Wilde.) |
#20
|
|||
|
|||
Elliptical Chainrings
On 19/07/2013 10:45 AM, none Yannick Tremblay wrote:
In article , Steve Freides wrote: Mower Man wrote: Isn't it the point that elliptical chain rings actually vary the gear ratio? Forget the number of teeth, they're only there 'cos a chain is used. Think of diameter. Variable diameter. Honest. Think drive belt? Big pulley vs small pulley? But big pulley versus small pulley, first of all, means something different for belt drive than for one with teeth. If one pedal revolution gets you 39 teeth spaced evenly apart, what's the difference what the shape is? For a belt driven system, a change in shape could at least mean a change in circumference. For 1 complete revolution, there is no difference. Absolutely correct. However what about 1/4 of a revolution or 1/8 of a revolution? Then the diameter of the "big pulley" does differs. Yan Spot on. That's how it works. -- Chris 'Fashion is a form of ugliness so intolerable that we have to alter it every six months.' (Oscar Wilde.) |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
New Schwinn 438 Elliptical Trainer! Highly Recommend! | rapee | Techniques | 0 | May 28th 08 07:39 AM |
New Schwinn 438 Elliptical Trainer! Highly Recommend! | rapee | Techniques | 0 | May 28th 08 07:38 AM |
Precor Elliptical: Watts vs Cyclist's? | (PeteCresswell) | Techniques | 3 | January 21st 08 09:08 PM |
How to quiet elliptical? | Dan | Techniques | 2 | November 13th 07 08:44 PM |
Headlight that mounts on Elliptical Handlebar ? | swamprun | Techniques | 5 | May 24th 06 03:21 AM |