J
jim beam
Guest
[email protected] wrote:
> Andres Muro wrote:
>
>>>> I should have added that Damon Rinard has a long FEA page about strain
>>>> energy and how it's stored in frames:
>>>> http://www.sheldonbrown.com/rinard/fea.htm
>
>>>> A few passages of interest...
>
> # The true intent of a stiff frame is to transfer energy efficiently
> # from the cyclist to the rear wheel. This implies that the designer
> # should minimize the amount of energy that goes into flexing
> # (straining) the frame. Some of this strain energy might be
> # recoverable (i.e., released in such a way as to add power to the
> # rear wheel). But we know of no measurements that show how much is
> # recovered. Thus, we assume that the best policy is to minimize
> # strain energy absorption in the frame.
>
>>>> [That is, how much of the energy is recovered is unknown.]
>
> # First, note that the start-up (or hill-climbing) load generates the
> # highest level of energy storage. The energy stored here (79.5 in-lb)
> # represents about 4.0 percent of the rider's total energy output
> # under typical hill-climbing conditions. This might sound like a
> # small percentage, but in racing situations, even a slight reduction
> # in this percentage would be noticed.
>
>>>> [That is, hill-climbing and start-up would be where things might
>>>> be noticed, not the familiar case of "snap" out of corners. And
>>>> frame differences will be trying to change a maximum loss of 4% of
>>>> the rider's effort--meaning that a frame twice as efficient could
>>>> save a maximum 6 watts at 300 watts, and less than that if any
>>>> energy is recovered.]
>
>>> ISTM that there is evidence that either much of the strain energy
>>> is recovered, or at least that down tube strain energy does not
>>> significantly sap acceleration.
>
>>> My thought processes went like this:
>
>>> One could build some racing bikes with absurdly stiff down tubes,
>>> and race them in competition with more normal bikes. If the
>>> absurdly stiff frames didn't strongly dominate, that would be
>>> evidence that down tube energy absorption wasn't a strong effect.
>
>>> Then I thought: Oh yeah. That's been done. By Cannondale.
>
>>> Cannondale was successful enough with their early '90s (was it?)
>>> frames, with downtubes that looked like cannons. But they weren't
>>> so successful that everybody else jumped on the absolutely-massive-
>>> downtube wagon. They weren't seen as magic bullets - just another
>>> good, trendy bike for those who liked them.
>
>>> BTW, there is a completely opposite viewpoint out there. Jan
>>> Heine, in his "Bicycle Quarterly" magazine, compliments many frames
>>> for their mysterious "planing" action. It's a word he uses for
>>> some mystical synchronizing between frame flex and rider input. He
>>> maintains that if a frame doesn't have the so-far-unexplained flex,
>>> the rider never "gets on top of the gear" and is significantly
>>> slower. He's absolutely against super-rigid bikes, from what I can
>>> tell.
>
>>> I get the impression that, as in lots of bike technology, there's
>>> lots of "magic" at work. Some of the incantations involve
>>> ill-defined words and indescribable feelings. Other incantations
>>> involve inscrutable numerology. ;-)
>
>> In fact during the 80s and 90s most pros used to ride Italian steel
>> frames or French aluminum frames. The French aluminum frames were
>> known for being very soft. Pros who rode the French Vitus frames
>> were apparently not at any disadvantage over the stiffer Columbus
>> SLX and max tubed frames. If there was a proven advantage of stiff
>> vs soft frames everyone would ride the stiffer ones. In fact, many
>> pros would disguise the softer Vitus frames as the stiff steel
>> frames if their sponsors required them to ride the Italian stiff
>> stuff.
>
>> This argument has been around at least since I started riding in the
>> early 80s. Magazines would always compliment stiffer frames and ads
>> would always pronounce the superiority of their stiffer frames.
>> However, I haven't read any article that proves that stiffer is
>> better and my own experience is that I don't get any faster with a
>> stiffer or softer frame.
>
> As you see, impractical engineers and others have long supported the
> frame flex energy losses with nothing but hot air.
as usual jobst, you take one tiny part of the picture, then hold that up
as the whole story. while you are correct, there is effectively no
hysteresis in a metal frame and thus no frame loss, a frame that flexes
will have wheels out of plane at the time of flex, thus more scrub, thus
more energy dissipated. real simple if you can be bothered to get off
your high horse for just a second.
> I recall when
> there were the steel frames getting soft after a year or so of racing
red herring.
> and tubular tires needing to be bought in the off season to be aged".
rubber does indeed age - it continues to cross-link. the question is
whether that is beneficial...
> These all boil down to sales gimmicks and riders eat it with a spoon
> and retell what they have learned from "reliable sources".
what? like "reliable sources" that contend that metal fatigue can be
eliminated from stainless steel, a material with no fatigue endurance
limit? or "reliable sources" that contend that calculation of spoke
load is somehow a calculation evidencing wheel strength?
>
> It's like the old saw that Campagnolo Record brakes (the finest ever
> made both for use and maintenance) were not made to stop but rather to
> modulate speed of racers who didn't need to stop. If you believe
> that, you are unaware that for fast (descents and the like) the faster
> the harder the brakes are used. Because the complaining wimps had
> much cash, the bicycle industry upped the MA and gave us the less
> functionally good dual pivot brake (big cosine error and pad drag on
> climbs) increased the MA (by reducing pad clearance).
>
> We must relive all these ploys because the new generation of riders is
> no smarter than the old in detecting BS.
and thus, we have a knowledge gap into which "the bicycle wheel" can be
sold. when are you going to start correcting its fundamental errors?
> Andres Muro wrote:
>
>>>> I should have added that Damon Rinard has a long FEA page about strain
>>>> energy and how it's stored in frames:
>>>> http://www.sheldonbrown.com/rinard/fea.htm
>
>>>> A few passages of interest...
>
> # The true intent of a stiff frame is to transfer energy efficiently
> # from the cyclist to the rear wheel. This implies that the designer
> # should minimize the amount of energy that goes into flexing
> # (straining) the frame. Some of this strain energy might be
> # recoverable (i.e., released in such a way as to add power to the
> # rear wheel). But we know of no measurements that show how much is
> # recovered. Thus, we assume that the best policy is to minimize
> # strain energy absorption in the frame.
>
>>>> [That is, how much of the energy is recovered is unknown.]
>
> # First, note that the start-up (or hill-climbing) load generates the
> # highest level of energy storage. The energy stored here (79.5 in-lb)
> # represents about 4.0 percent of the rider's total energy output
> # under typical hill-climbing conditions. This might sound like a
> # small percentage, but in racing situations, even a slight reduction
> # in this percentage would be noticed.
>
>>>> [That is, hill-climbing and start-up would be where things might
>>>> be noticed, not the familiar case of "snap" out of corners. And
>>>> frame differences will be trying to change a maximum loss of 4% of
>>>> the rider's effort--meaning that a frame twice as efficient could
>>>> save a maximum 6 watts at 300 watts, and less than that if any
>>>> energy is recovered.]
>
>>> ISTM that there is evidence that either much of the strain energy
>>> is recovered, or at least that down tube strain energy does not
>>> significantly sap acceleration.
>
>>> My thought processes went like this:
>
>>> One could build some racing bikes with absurdly stiff down tubes,
>>> and race them in competition with more normal bikes. If the
>>> absurdly stiff frames didn't strongly dominate, that would be
>>> evidence that down tube energy absorption wasn't a strong effect.
>
>>> Then I thought: Oh yeah. That's been done. By Cannondale.
>
>>> Cannondale was successful enough with their early '90s (was it?)
>>> frames, with downtubes that looked like cannons. But they weren't
>>> so successful that everybody else jumped on the absolutely-massive-
>>> downtube wagon. They weren't seen as magic bullets - just another
>>> good, trendy bike for those who liked them.
>
>>> BTW, there is a completely opposite viewpoint out there. Jan
>>> Heine, in his "Bicycle Quarterly" magazine, compliments many frames
>>> for their mysterious "planing" action. It's a word he uses for
>>> some mystical synchronizing between frame flex and rider input. He
>>> maintains that if a frame doesn't have the so-far-unexplained flex,
>>> the rider never "gets on top of the gear" and is significantly
>>> slower. He's absolutely against super-rigid bikes, from what I can
>>> tell.
>
>>> I get the impression that, as in lots of bike technology, there's
>>> lots of "magic" at work. Some of the incantations involve
>>> ill-defined words and indescribable feelings. Other incantations
>>> involve inscrutable numerology. ;-)
>
>> In fact during the 80s and 90s most pros used to ride Italian steel
>> frames or French aluminum frames. The French aluminum frames were
>> known for being very soft. Pros who rode the French Vitus frames
>> were apparently not at any disadvantage over the stiffer Columbus
>> SLX and max tubed frames. If there was a proven advantage of stiff
>> vs soft frames everyone would ride the stiffer ones. In fact, many
>> pros would disguise the softer Vitus frames as the stiff steel
>> frames if their sponsors required them to ride the Italian stiff
>> stuff.
>
>> This argument has been around at least since I started riding in the
>> early 80s. Magazines would always compliment stiffer frames and ads
>> would always pronounce the superiority of their stiffer frames.
>> However, I haven't read any article that proves that stiffer is
>> better and my own experience is that I don't get any faster with a
>> stiffer or softer frame.
>
> As you see, impractical engineers and others have long supported the
> frame flex energy losses with nothing but hot air.
as usual jobst, you take one tiny part of the picture, then hold that up
as the whole story. while you are correct, there is effectively no
hysteresis in a metal frame and thus no frame loss, a frame that flexes
will have wheels out of plane at the time of flex, thus more scrub, thus
more energy dissipated. real simple if you can be bothered to get off
your high horse for just a second.
> I recall when
> there were the steel frames getting soft after a year or so of racing
red herring.
> and tubular tires needing to be bought in the off season to be aged".
rubber does indeed age - it continues to cross-link. the question is
whether that is beneficial...
> These all boil down to sales gimmicks and riders eat it with a spoon
> and retell what they have learned from "reliable sources".
what? like "reliable sources" that contend that metal fatigue can be
eliminated from stainless steel, a material with no fatigue endurance
limit? or "reliable sources" that contend that calculation of spoke
load is somehow a calculation evidencing wheel strength?
>
> It's like the old saw that Campagnolo Record brakes (the finest ever
> made both for use and maintenance) were not made to stop but rather to
> modulate speed of racers who didn't need to stop. If you believe
> that, you are unaware that for fast (descents and the like) the faster
> the harder the brakes are used. Because the complaining wimps had
> much cash, the bicycle industry upped the MA and gave us the less
> functionally good dual pivot brake (big cosine error and pad drag on
> climbs) increased the MA (by reducing pad clearance).
>
> We must relive all these ploys because the new generation of riders is
> no smarter than the old in detecting BS.
and thus, we have a knowledge gap into which "the bicycle wheel" can be
sold. when are you going to start correcting its fundamental errors?
