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PostPosted: Wed Dec 07, 2011 11:27 pm 
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Tubbie Guru

Joined: Tue May 03, 2005 2:20 am
Posts: 5851
Location: Belgium
Hi,

Quote:
In addition the rear wheel will experience torque loads which will reduce tension on all pushing spokes. So the lateral stiffness of these rims would be worse (maybe a lot worse) in practice than what is shown on these graphs. Determining just how much difference would take more analysis. Some might already be past the point where the stiffness rapidly declines


Exactly. :thumbup:
Those wheels are reserved for featherweights only and then some.

Ciao, ;)

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Posted: Wed Dec 07, 2011 11:27 pm 


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PostPosted: Thu Dec 08, 2011 9:40 am 
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WWotY 2007
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Joined: Sat Jul 10, 2004 5:37 pm
Posts: 1476
Location: France.
rruff wrote:
A note about the rims that exhibit this behavior: On the road, the same spokes that are subject to lateral loads (at the bottom of the wheel) will already have their tension reduced due to holding the bike and rider up. In addition the rear wheel will experience torque loads which will reduce tension on all pushing spokes. So the lateral stiffness of these rims would be worse (maybe a lot worse) in practice than what is shown on these graphs. Determining just how much difference would take more analysis. Some might already be past the point where the stiffness rapidly declines.


Thanks a million rruff for this nice input. :thumbup:
The spokes on such a wheelset do not have any tension. They merely work with 0 tension at rest, and deal with some tension/compression loads that depends on the rider weight at each wheel revolution.

It would be nice to see what happens with a load from the bottom of the wheel in addition to the lateral one.
I'm not sure it would obligatory reduce the lateral stiffness.
Indeed the bottom load would tend to put some compression on the spokes near this load. These spokes will tend to bend for sure, but this would happen to both sides of the wheel, not only the side where the lateral load is applied.
Thus, while the spoke on one side of the wheel bends and has lost stiffness due to bending, the one on the other side has bent too but in the opposite sense. So before losing its stiffness while bending again on the other side, it has to come back to standard position where it is stiff.

Regarding the torque loads, the central flange is supposed to deal with this while gaining tension. It must not be part of the lateral testings I think.

Epic-o wrote:
Adrien, Do you know what are the typical lateral loads during standing pedaling? I tried to do some calculations but it's not as simple as I thought


This can be determined through some trigonometric formulas. We know rider weight, weight distribution on both wheels, wheel angle with the ground, and the direction of the lateral load. Put these info into the right formula ;)

This result could be controlled as a real application with a known rider/bike weight, the right distance from brake pads to rims, and a marker on the brake pads. If the rim is marked, it rubbed the pads. We could check with the 180° data measured on the bench.
I must say that I didn't have time to perform such a test yet.

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PostPosted: Thu Dec 08, 2011 10:30 am 
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Joined: Tue Nov 20, 2007 7:18 pm
Posts: 621
Adrien wrote:
This can be determined through some trigonometric formulas. We know rider weight, weight distribution on both wheels, wheel angle with the ground, and the direction of the lateral load. Put these info into the right formula ;)

This result could be controlled as a real application with a known rider/bike weight, the right distance from brake pads to rims, and a marker on the brake pads. If the rim is marked, it rubbed the pads. We could check with the 180° data measured on the bench.
I must say that I didn't have time to perform such a test yet.


I have seen the graph that you showed in your web and if you decompose the force components that you drew in the wheel's frame you will notice that the lateral load on the rim is 0. Your scheme doesn't consider lateral movement of the rider while standing pedalling, something pretty strange because if you have a lateral load on the bicycle it should cause a lateral acceleration, don't you think?
My first thought is that lateral loads are generated by a combination of lateral acceleration of the bicycle (rider is pretty much static laterally) and side slip forces generated during the lateral movelment while standing pedaling. There is also lateral loads generated by the drivetrain but that's another story.

Salut

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PostPosted: Thu Dec 08, 2011 6:00 pm 
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Joined: Sun Jan 08, 2006 9:12 am
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Location: Alto, NM
Adrien wrote:
Indeed the bottom load would tend to put some compression on the spokes near this load. These spokes will tend to bend for sure, but this would happen to both sides of the wheel, not only the side where the lateral load is applied.
Thus, while the spoke on one side of the wheel bends and has lost stiffness due to bending, the one on the other side has bent too but in the opposite sense. So before losing its stiffness while bending again on the other side, it has to come back to standard position where it is stiff.


I think it might be worse. In a pure lateral test, one side adds tension when the other is slack, while with a radial load added, both sides could start out slack. After deflecting a certain amount, one side would have tension again and the steep slope in your test would be replicated. But it is also likely that more spokes at the bottom of the wheel would be effected (slack)... which would make it even worse again.

The Aerozenith, Lew, Reynolds, Corima, and Obermeyer exhibit this to some degree. I'm guessing the Obermeyer has pretension, but that is not so high. The Corima has very fat spokes so it takes a significant load before they buckle. The spokes on the others must buckle at very light loads, so are likely to already be buckled due to radial weight.

Seems like an odd (and undesirable) way to design a wheel...


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PostPosted: Fri Dec 09, 2011 12:16 pm 
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Massive thanks Adrien! Always an interesting read!

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