Is an aero frame beneficial? (light or aero bike faster?)

Discuss light weight issues concerning road bikes & parts.
goodboyr
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by goodboyr

andy2 wrote:http://s730.photobucket.com/albums/ww301/andy2-photos/?action=view&current=bb-movie1.mp4" onclick="window.open(this.href);return false;

Above is a link to an illustration of a load case of our frame with an overly soft layup for illustration. Here it is loaded 100 kg applied at the drive side pedal.
We are using Altair Hyper Works FEA, with is the leading industry analysis tool as used by MacLaren and others.
You are viewing the frame from the rear nds. The flex is magnified, again for illustration, but the impact is clear. The frame will flex in a manner that will not be contained or harvested by the drivetrain, resulting in forward propulsion. The work done flexing the carbon spring/frame is essentially lost and dissipated through heat in the engine/pilot/cyclist. If we could harvest this flex in the manner of a trampoline or bow as suggested by some we would have an instant ban by the UCI on our hands...
The other effect that is clear from the illustration is how the rear wheel will 'crab' under load. This is akin to the crabbing of an airplane and is of course resulting in a loss of efficiency.
To infuse the discussion with a measure of rocket surgery: Rockets are fired straight up for this very reason. :up:

/a


So, let me get this straight. You've got the frame flexing back and forth in this model, and thus by observation you now feel you've proven your hypothesis. Sorry, but this doesn't add anything at all to the discussion. If there rear wheel "crabbed" as you said, flexible frames would be skidding across the road, you'd wear out your tires, and the effect would be easily felt. And the tire, road interface is being completely ignored here.
Tanhalt, please take over!

by Weenie


tanhalt
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by tanhalt

goodboyr wrote:Tanhalt, please take over!


I have only one thing to say in regards to that "analysis": Boundary conditions and load paths :roll:

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dj97223
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by dj97223

tanhalt wrote:
goodboyr wrote:Tanhalt, please take over!


I have only one thing to say in regards to that "analysis": Boundary conditions and load paths :roll:


I'm no scientist, but I think you actually just said "two" things. :smartass:
“If you save your breath I feel a man like you can manage it. And if you don't manage it, you'll die. Only slowly, very slowly, old friend.”

Epic-o
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Joined: Tue Nov 20, 2007 7:18 pm

by Epic-o

I think you are trying to find an easy answer to a very difficult problem. Power dissipation induced by dynamic elastic strain of the rear end of a bike involves many variables whose combined influence nobody have studied: damping of carbon fiber, damping in the chain, lateral sliping of the wheel, increase in chain friction losses, etc

One thing is sure, to ride a stiff, comfortable frame gives you a psychological advantage.

tanhalt
Posts: 109
Joined: Wed Dec 27, 2006 6:36 pm

by tanhalt

dj97223 wrote:
tanhalt wrote:
goodboyr wrote:Tanhalt, please take over!


I have only one thing to say in regards to that "analysis": Boundary conditions and load paths :roll:


I'm no scientist, but I think you actually just said "two" things. :smartass:


It's a single comment :P

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horse
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Joined: Sun Oct 09, 2011 1:09 pm

by horse

You gyus must take people for fools.

Boundary Conditions, so what? You simply arrange the data on the model and let simulate conditions on the model.

To the other rocket guy.. crap analogy. Maybe you know a reason for rockets going sideways. Lmao.

All this says absolutely nothing about benefits of aero frame. There are Pros and Cons to specific design. Be it a profiled aero frame or a traditional/standardized rig. There is no blanket answer which is better or beneficial. Both have their uses/benefits. An aero frame will typically be profiled in the vertical dimension, while a stiff bike will be in the horizontal. When you do this you get opposing results because a frame profiled vertically will not have the comparable torsional stiffness.
The moral of the story is to blend the two notions together in a compromise.

goodboyr
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Location: Canada

by goodboyr

horse wrote:You gyus must take people for fools.

Boundary Conditions, so what? You simply arrange the data on the model and let simulate conditions on the model.

To the other rocket guy.. crap analogy. Maybe you know a reason for rockets going sideways. Lmao.

All this says absolutely nothing about benefits of aero frame. There are Pros and Cons to specific design. Be it a profiled aero frame or a traditional/standardized rig. There is no blanket answer which is better or beneficial. Both have their uses/benefits. An aero frame will typically be profiled in the vertical dimension, while a stiff bike will be in the horizontal. When you do this you get opposing results because a frame profiled vertically will not have the comparable torsional stiffness.
The moral of the story is to blend the two notions together in a compromise.


No comment. You are way too smart for the rest of us. :twisted: :roll:

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prendrefeu
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by prendrefeu

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justkeepedaling
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by justkeepedaling

horse wrote:You gyus must take people for fools.

Boundary Conditions, so what? You simply arrange the data on the model and let simulate conditions on the model.

To the other rocket guy.. crap analogy. Maybe you know a reason for rockets going sideways. Lmao.

All this says absolutely nothing about benefits of aero frame. There are Pros and Cons to specific design. Be it a profiled aero frame or a traditional/standardized rig. There is no blanket answer which is better or beneficial. Both have their uses/benefits. An aero frame will typically be profiled in the vertical dimension, while a stiff bike will be in the horizontal. When you do this you get opposing results because a frame profiled vertically will not have the comparable torsional stiffness.
The moral of the story is to blend the two notions together in a compromise.


I'm not sure if you've ever done any Finite Element Analysis but boundary conditions, load paths, and magnitudes that accurately portray the system are EVERYTHING. You can get completely different results just by changing a single variable or using a different node.

thisisatest
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by thisisatest

with all due respect to damon rinard, i feel his test didnt answer the question. it answered whether or not the frame was absorbing energy (which it essentially does not). it did not test whether the rider had to expend more energy for the same end result.
a frame twisting, moving the bottom bracket to the side, lowers that side's pedal. hence, the extra distance traveled. that frame flex does not return to the drivetrain. at the bottom of the pedal stroke, you can bounce up and down all you want but it wont turn the cranks. i understand that a lot of potential points for flex would simply return into the drivetrain, i am trying to point out that this is not one of them.
an ideal test would be to test one rider on two frames using the same power meter (or two meters tested to read identically) and just see what power output he has for a given heart rate or oxygen uptake or whatever.

jsinclair
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Location: Sydney, Australia

by jsinclair

This might be a little off topic but if you had a set up that included an SRM crank and a powertap hub and calibrated them to match for a given control bike, could you move this system from frame to frame and test the variation between the power in and power out for various bikes? I assume the error would be the 2% SRM claims?

maxxevv
Posts: 1958
Joined: Wed Feb 09, 2005 4:51 am

by maxxevv

jsinclair wrote:This might be a little off topic but if you had a set up that included an SRM crank and a powertap hub and calibrated them to match for a given control bike, could you move this system from frame to frame and test the variation between the power in and power out for various bikes? I assume the error would be the 2% SRM claims?


No, you won't get a correct answer anyway. Because net input into the frame and net output is not differentiated by the SRM, since it only measures input.

If you want to really measure then perhaps you need to add in a treadmill with power measuring capabilities as a turbo trainer won't cut it either, since the rear axle is fixed in position. The treadmill would measure the output from the bike/frame in question while the SRM would measure the input. Only when you have differentiated input and output measurements, then can you tell the difference between them in terms of losses.

But this is in the context of power losses purportedly from frame flex.

For aerodynamics differences, its actually a whole lot easier. All you need a is motor powered hub with a calibrated motor that churns out a specific power output that can be recorded. And a speed readout that can be coordinated with the readout from this motor (hub). Mount this onto the aero frames in question and run them on a velodrome and compare. For a specific power input, the differences in speed. And vice versa, a specific speed, the differences in power input. :beerchug:

goodboyr
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Location: Canada

by goodboyr

thisisatest wrote:with all due respect to damon rinard, i feel his test didnt answer the question. it answered whether or not the frame was absorbing energy (which it essentially does not). it did not test whether the rider had to expend more energy for the same end result.
a frame twisting, moving the bottom bracket to the side, lowers that side's pedal. hence, the extra distance traveled. that frame flex does not return to the drivetrain. at the bottom of the pedal stroke, you can bounce up and down all you want but it wont turn the cranks. i understand that a lot of potential points for flex would simply return into the drivetrain, i am trying to point out that this is not one of them.
an ideal test would be to test one rider on two frames using the same power meter (or two meters tested to read identically) and just see what power output he has for a given heart rate or oxygen uptake or whatever.


But that's the whole point. You seem to be concluding by obswrvation what the test will show without doing the test.

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kgt
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Location: Athens, Greece

by kgt

I think that all this lightness, stifness and aero marketing will soon come to an end. Almost every modern frame can be light, stiff and aero. Even the frames of the smallest manufacturers. I think we have to concentrate on the ride quality more and - last but not least - push the prices down and make top bikes available to more people. IMO it is unacceptable for a modern carbon frame to cost 5000 or 6000 euros. You get a nice scooter with this amount of money.

Franklin
Posts: 400
Joined: Mon Aug 04, 2008 11:09 am

by Franklin

andy2 wrote:http://s730.photobucket.com/albums/ww301/andy2-photos/?action=view&current=bb-movie1.mp4" onclick="window.open(this.href);return false;

Above is a link to an illustration of a load case of our frame with an overly soft layup for illustration. Here it is loaded 100 kg applied at the drive side pedal.
We are using Altair Hyper Works FEA, with is the leading industry analysis tool as used by MacLaren and others.
You are viewing the frame from the rear nds. The flex is magnified, again for illustration, but the impact is clear. The frame will flex in a manner that will not be contained or harvested by the drivetrain, resulting in forward propulsion. The work done flexing the carbon spring/frame is essentially lost and dissipated through heat in the engine/pilot/cyclist. If we could harvest this flex in the manner of a trampoline or bow as suggested by some we would have an instant ban by the UCI on our hands...
The other effect that is clear from the illustration is how the rear wheel will 'crab' under load. This is akin to the crabbing of an airplane and is of course resulting in a loss of efficiency.
To infuse the discussion with a measure of rocket surgery: Rockets are fired straight up for this very reason. :up:

/a


Andy2 comparing a rocket with a bike is ludicrous as the whole dynamics are different.

The best answer why this model is not enough to answer this question is the simple admission of solid wheels versus wheels with tires.

Solid wheels have less flex and don't deform, so they are much faster... except they aren't, solid wheels are absolutely crap. Quite simply, flex does not equal speed loss.

A few things about which I have absolutely confidence are true:

1. Cornering a "horizontally infinitely stiff bike" will suck compared to a normal bike.
2. Even speed on a strait stretch on a horizontally infinitely stiff bike is less than that of a normal bike.
3. Aero (Moser, Obree, Boardman) gave bigger speed gains than stiffness. In fact, Moser's bike most likely was a complete noodle with it's thin Columbus tubing.
4. Frame flex is countered and made worse by body flex. The joints of the cyclist are not static. When a rider flexeshis frame, he also will flex his body. It remains to be seen if taking away the flex in the frame simply means all that flex will all of a sudden become forward speed instead of being transmitted towards the riders body. Considering the solid wheel versus wheel with tire evidence the latter is certainly an issue.

Sure, a bike certainly can be to flexible, but nowadays that is extremely rare (some exotic titanium). Considering the speeds reached on much, much more flexible frames than we have now it's extremely hard to maintain that stiffness is a big issue.

Sorry Andy, the notion that the gains of having an infinitely stiff drivetrain offsets the bad handling and comfort issues simply don't seem to be true. The real world evidence overwhelmingly suggests a bike needs to be flexible.

by Weenie


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