High stiffness and performance gain

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WMW
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by WMW

jano wrote:Elastic deformation of the frame means that energy is being used for something else then moving your bike forward.
A large part of the energy, not 100% of it, that was used to produce an amount of deformation will be returned generally to the rider's body, this will generally result in some fatigue due to the need for the core muscles to compensate for absorbing that returned energy.
The only time energy that generates deformation is returned and results in forward movement is when it happens in the drive train.


Nonsense. The flex that occurs as force is ramped up, gets returned as force ramps down. It doesn't mysteriously "go into the rider's body" it simply modifies the force/motion curve slightly.
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WMW
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by WMW

TheKaiser wrote:Thus, the lateral deflection will be peaking during the dead point


Max deflection is at the point of max force. ~100 degrees in the stroke. In the "dead zone" the position will pass through neutral.
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shlammed
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by shlammed

I had a flexy old steel bike and and still have my much stiffer giant TCR. I was just as fast on the steel bike on strava segments where I didn't have to change gears (the STI levers on the tcr are much better than the downtube shifters were in that case).


Unless your loosing races by a second or two, its not the bikes fault. I would personally get a bike that HAS a little more flex that Im not too big for and would bend/shatter. Consider that im not racing though, so that comment is for comfort.

jano
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by jano

WMW wrote:
jano wrote:Elastic deformation of the frame means that energy is being used for something else then moving your bike forward.
A large part of the energy, not 100% of it, that was used to produce an amount of deformation will be returned generally to the rider's body, this will generally result in some fatigue due to the need for the core muscles to compensate for absorbing that returned energy.
The only time energy that generates deformation is returned and results in forward movement is when it happens in the drive train.


Nonsense. The flex that occurs as force is ramped up, gets returned as force ramps down. It doesn't mysteriously "go into the rider's body" it simply modifies the force/motion curve slightly.


Lots of bla bla mate. Along with your claims that frame flex can be returned into forward movement, which is what we are all after when we get on a bike.
What about you put pen on paper and show us some of your calculations about how vertical or lateral flex of a bike frame magically becomes forward movement of a bike? Then we talk again.

Until then I stay by my conclusion, based on what I learned as an engineer, and that is that part of the energy that produces flex in the frame is returned and will be absorbed by the rider who is the only part of the bike/rider whole that has a dynamic adaptive function, unless you ride one of those Time Aktiv frames with a mass damper built into the fork.

jano
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by jano

Alternatively you could can save yourself a lot of time and just do an empiric test by replacing your cranks with a straight tube, stand on it and induce flex into the frame by shifting your weight from left to right and back. Let us know the longitudinal speed you achieved by doing this.
PS: obviously you should do it on a flat not on a slope.

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WMW
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by WMW

jano wrote:What about you put pen on paper and show us some of your calculations about how vertical or lateral flex of a bike frame magically becomes forward movement of a bike? Then we talk again. Until then I stay by my conclusion, based on what I learned as an engineer, and that is that part of the energy that produces flex in the frame is returned and will be absorbed by the rider who is the only part of the bike/rider whole that has a dynamic adaptive function, unless you ride one of those Time Aktiv frames with a mass damper built into the fork.


You need to attempt to do some calculations so you can understand why there is nothing there. The spring in the system just changes the force and response curve slightly. When it is springing back, the rider is still applying motive force to the system.

jano wrote:Alternatively you could can save yourself a lot of time and just do an empiric test by replacing your cranks with a straight tube, stand on it and induce flex into the frame by shifting your weight from left to right and back. Let us know the longitudinal speed you achieved by doing this.


Your simplified example unfortunately doesn't model what is happening. No need to simplify. Our "bar" is a crank that's attached to a chain drive. When force is applied to make the cranks go around, the frame absorbs some of that energy by moving away from the force. When the force declines, the frame returns it by moving back to where it was.

If it helps you could simplify it by looking just at the crank and assume a sinusoidal tangential force is applied to it, and flexes like a spring. The frame is doing the same thing, it's just more complicated.
Last edited by WMW on Thu Jul 30, 2015 5:52 am, edited 1 time in total.
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kulivontot
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by kulivontot

I've yet to see calculations in this thread, so I don't know whose hand waving analysis to believe more.

LetsRide
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by LetsRide

This GCN test setup seems similar to what I am looking for. Actually, a part of stiffness test was already done in the test including weight test. It is not a perfectly controlled test but it should be good to see some initial results.

Light Bike Vs. Heavy Bike – What's The Difference On A Climb? GCN Does Science
https://www.youtube.com/watch?v=le_LSWfGJUo

Perhaps, some new things could be learned e.g. super stiff bike probably could outperform a 200g-lighter bike with average stiffness on a steep climb or a sprint, who knows ? Or if it turned out that stiffness did not affect performance at all, then it should be a good thing to know also IMHO.

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WMW
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by WMW

LetsRide wrote:This GCN test setup seems similar to what I am looking for.


Bad testing. Worse than no test at all.
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LetsRide
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by LetsRide

Even only one bad test, there should be some input to discuss which part of the test is good or bad. And it could spark up others to do similar tests. So far, without a formal test, I only have to use imagination what the results should be.

Please feel free to share test results for anyone who has tools ready. Or try persuading others who can conduct a test. Thank you everyone.

TheKaiser
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by TheKaiser

WMW wrote:
TheKaiser wrote:Thus, the lateral deflection will be peaking during the dead point


Max deflection is at the point of max force. ~100 degrees in the stroke. In the "dead zone" the position will pass through neutral.


I overstated, based on the evidence I cited, when I said "peaking", thank you for the correction. What I was taking into account was that, even though max force is at 100 degrees, as the crank arm swings down toward 6 o'clock the length of the lever flexing the BB sideways increases so, even though force is lower, leverage is greater. I don't however have the figures to model this interplay of somewhat lower force multiplied by a substantially longer lever, however the rapidly increasing lever length lead me to believe that it would more than offset the less rapidly decreasing force.

This all applies to lateral flex at the BB and torsional flex in the front triangle, but would not apply to some of the flex in the rear triangle which is generated by the compressive forces of the chain.

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WMW
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by WMW

TheKaiser wrote:I overstated, based on the evidence I cited, when I said "peaking", thank you for the correction. What I was taking into account was that, even though max force is at 100 degrees, as the crank arm swings down toward 6 o'clock the length of the lever flexing the BB sideways increases so, even though force is lower, leverage is greater.


The lateral distance between the force vector (the pedal) and the centerline of the bike is constant. That's the one causing the BB to flex sideways.
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LetsRide
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by LetsRide

Cycling Weekly just tested "How does weight affect your climbing speed? (video)"
http://www.cyclingweekly.co.uk/news/lat ... deo-186771

I wish I could see tests on stiffness in the near future.

Franklin
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by Franklin

WMW wrote:Nonsense. The flex that occurs as force is ramped up, gets returned as force ramps down. It doesn't mysteriously "go into the rider's body" it simply modifies the force/motion curve slightly.


Wait... what's so magical of the flex being directed towards the rider? And what's magical about the body acting as a dampener?

I'm certain some flex will be dampened by the rider. The question is how much. But denying that the body will act as a dampener without any model showing how (almost) everything simply goes back into the drivetrain (talk about magic!) is truly cutting corners here.

I'm not convinced of your position, however much I respect your knowledge on cycling parts.

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jadekim
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by jadekim

eric wrote:I haven't seen any tests either. Since the frame is a spring, most of the energy that goes into bending it will be returned. The problem is that it's returned via the crank and pedals to the rider. That's where it gets difficult to understand, model or measure.


i understand your opinion.
but i think doesn't have any standard way of evaluation for stiffness ?

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