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Back in the day.... Sean Kelly raced and won many a sprint on an aluminum Vitus frame:
http://www.seankelly.com/index.php# This frame was reputed to be one of the most flexable modern racing frames ever produced. |
Originally Posted by slowandsteady
Stiffer frames are faster. Just ride a mountain bike with a full suspension for proof. But, that said, is the difference from the flexiest road frame to the stiffest road frame enough to be statistically significant....who knows.
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Originally Posted by galen_52657
Back in the day.... Sean Kelly raced and won many a sprint on an aluminum Vitus frame:
http://www.seankelly.com/index.php# This frame was reputed to be one of the most flexable modern racing frames ever produced. |
Originally Posted by Grasschopper
Back in the day the Indy 500 was won with 50hp engines...what is your point here exactly? .
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Forgetting about comfort and how a less stiff frame keeps the rider feeling better and perhaps pedalling better, a stiffer frame is faster. For any given level of power output, maximum efficiency occus when 100% is used to turn the rear wheel. When frame flex occurs, that uses energy. Less than 100% is being transmitted to make the bike go forward.
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Originally Posted by 531Aussie
inappropriate analogy. 'Back in the day' everyone had 50hp engines, but the perception was that Kelly was at a big disadvantage riding a frame that reportedly felt like wet spaghetti while everyone else was on super-stiff Columbus MAX (etc) frames. Despite having a sloppy bike, Kelly kept winning races.
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Originally Posted by merlinextraligh
However, to the extent the frame rebounds, the energy isn't lost, except to the extent of energy lost as heat in the process. Thus the amount of energy lost in frame flex that could be converted to speed has to be incredibly negligable.
I do think there are some perception things going on that may make a stiff frame feel faster, and may possibly even make the rider ride faster due to a confidence or motivational affect. Switching from my Merlinextralight, a relatively flexy frame by current standards, to a 2007 Giant TCR Advanced Team, a very stiff frame, The Giant feels like pushing on the pedals gives a more instant response, whereas the Merlin feels like it doesn't accelerate as fast initially. The positive feedback makes it feel faster, and possibly inspires you to ride it faster. Also I've noticed in fast descents, the Giant seems to carve turns better, and feel more secure in high speed turns. I attribute this in part to the stiffer frame. (Although I'm willing to consider that it may well be in my head). My confidence in the line carved with the stiffer frame gives me the confidence to corner faster. If you consider that flex may also affect alignment than you might loose more energy thru the bike going sideways than thru the actual energy put into the frame. |
I don't know if I agree that flexing a steel frame wastes energy. It basically is a spring so almost all and I mean a fractionally unnoticeable small amount, of the energy comes back.
I can tell a difference in the way my steel bike rides vs my AL bike but I don’t know if any one feels faster. You might even be able to work with the spring effect in your frame to get some pseudo ‘free’ energy back on your pedal stroke. |
Originally Posted by jfmckenna
I don't know if I agree that flexing a steel frame wastes energy. It basically is a spring so almost all and I mean a fractionally unnoticeable small amount, of the energy comes back.
JAH (Physics and Chemistry degrees) |
Originally Posted by StanSeven
Forgetting about comfort and how a less stiff frame keeps the rider feeling better and perhaps pedalling better, a stiffer frame is faster. For any given level of power output, maximum efficiency occus when 100% is used to turn the rear wheel. When frame flex occurs, that uses energy. Less than 100% is being transmitted to make the bike go forward.
On a related subject, the road race motorcycle people understand all this after having gone too far toward the stiff side – designers are ADDING lateral flex into the frame and suspension since it reduces head shake and provides a suspension action to the frame when it’s laid over on it’s side in corners. A little lateral flex is a good thing; both for motorcycles and bicycles. |
Originally Posted by Nessism
The LAW of Conservation of Energy dictates that energy stored in the frame causing it to flex to one side on the down stroke is returned on the upstroke. The only energy loss is due to heat – which is negligible. Further, a frame that is killer stiff side to side can cause the rear tire to skip around and scrub off rubber due to slippage during a sprint; a slightly more flexible frame does not have this issue – it sort of smoothes out the power delivery to the rear wheel.
Wouldn't a flexy frame also allow the wheels you go somewhat out of alignment. If that happens you'll drift side to side with every pedal stroke, which definitely wastes energy. |
Stiff frames are slower because the fat tubes are less aero.
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I think if you make the assumption that the BB area is stiff enough to cause zero FD rubbing, then it's sufficiently stiff that power loss is negligible.
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I agree with Jeffrey. I see it like this.
1. You push down with your right foot, the bike "flexes" downward. This happens at the hardest push of your spin, when the pedals are parallel to the ground. 2. The bike then flexes upward, conservation of energy I get it. But by this point, your pedals aren't parallel to the ground, they're parallel to your downtube. Although the bike returns to it's unflexed position, this does NOT translate to forward motion. So to be more specific, the flex of the bike takes energy that could be used for forward motion, and translates it into vertical motion, this gets absorbed by the tires, you, or the frame. |
Originally Posted by merlinextraligh
However, to the extent the frame rebounds, the energy isn't lost, except to the extent of energy lost as heat in the process. Thus the amount of energy lost in frame flex that could be converted to speed has to be incredibly negligable.
Originally Posted by Bob Ross
Correction: celeste paint makes *riders* stiffer than red
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Originally Posted by Nessism
The LAW of Conservation of Energy dictates that energy stored in the frame causing it to flex to one side on the down stroke is returned on the upstroke. The only energy loss is due to heat – which is negligible.
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One other factor in a frame being faster is the beating a rider takes on a long ride. I recall seeing years ago that a more compliant frame was faster in use because the rider is uses less energy because they are less fatigued by road shock. Another case in that what works i the lab does not always work on the road.
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With all of this discussion about where frame flex ends up going -- back into the wheel, converted to heat and lost, etc -- let's consider the proportion of total power that is lost to flex. I would guess that even a frame that is considered "flexy" is really only dissipating (or not, if it is returned to the wheel) a teeny tiny portion of the rider's total output.
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Relating to personal experience last Thursday I know that a plush frame (Spec Roubaix) will vibrate like an old washing machine at 50 mph. Let me tell you , that will slow you down.
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Originally Posted by Coyote2
With all of this discussion about where frame flex ends up going -- back into the wheel, converted to heat and lost, etc -- let's consider the proportion of total power that is lost to flex. I would guess that even a frame that is considered "flexy" is really only dissipating (or not, if it is returned to the wheel) a teeny tiny portion of the rider's total output.
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Ok, as soon as my powertap comes back from Saris; I'll test it. One minute at say 300 watts on the Merlin, then one minute at 300 watts on the Giant. I'm willing to bet any difference won't be statistically significant.
Unfortunately, there will still be a few confounders, such as rider position, aerodynamics of the bikes themselves, gusts of wind, etc. But I'm betting even with those things there's not going to be a meaningful differnece. |
Originally Posted by curiouskid55
Relating to personal experience last Thursday I know that a plush frame (Spec Roubaix) will vibrate like an old washing machine at 50 mph. Let me tell you , that will slow you down.
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Originally Posted by merlinextraligh
Ok, as soon as my powertap comes back from Saris; I'll test it. One minute at say 300 watts on the Merlin, then one minute at 300 watts on the Giant. I'm willing to bet any difference won't be statistically significant.
Unfortunately, there will still be a few confounders, such as rider position, aerodynamics of the bikes themselves, gusts of wind, etc. But I'm betting even with those things there's not going to be a meaningful differnece. |
Originally Posted by merlinextraligh
Ok, as soon as my powertap comes back from Saris; I'll test it. One minute at say 300 watts on the Merlin, then one minute at 300 watts on the Giant. I'm willing to bet any difference won't be statistically significant.
Unfortunately, there will still be a few confounders, such as rider position, aerodynamics of the bikes themselves, gusts of wind, etc. But I'm betting even with those things there's not going to be a meaningful differnece. |
Originally Posted by galen_52657
Do the test on the trainer and check watts against heart rate. If frame flex is sapping power, the hear rate will be higher for the given power output. May have to do the test several times to average out factors like being tired, having a bad day at work, haven't gotten laid in a while...need to take a dump... you know...human factors...
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