Torsional stiffness wheel study?

Hi,

I'm wondering if anyone has done some kind of torsional wheel stiffness
study. That is how stiff the wheels are to resist the twisting that hard
out of the saddle climbing puts on them.

I've seen and read about lateral wheel stiffness studies, where the
deflection of the rim along the hub axis is measured when applying various
weights on the rim.

I'm considering a set of "aero" paired-spoke wheels and have been told by
the manufactor that: "Although the spoke count is low, the paired spoke
configuration makes for a very stiff wheel" and I was wondering how true
this statement is in the sense of measured deflections in degrees per
foot-pount of torque for various rim depth/spoke configurations ... or
something like that.

Thanks,

J.

kevinkiller wrote:
Hi,

I'm wondering if anyone has done some kind of torsional wheel stiffness
study. That is how stiff the wheels are to resist the twisting that hard
out of the saddle climbing puts on them.

I've seen and read about lateral wheel stiffness studies, where the
deflection of the rim along the hub axis is measured when applying various
weights on the rim.

I'm considering a set of "aero" paired-spoke wheels and have been told by
the manufactor that: "Although the spoke count is low, the paired spoke
configuration makes for a very stiff wheel" and I was wondering how true
this statement is in the sense of measured deflections in degrees per
foot-pount of torque for various rim depth/spoke configurations ... or
something like that.

Thanks,

J.

Torsional stiffness of the spoke complement can be calculated
approximately. Archibald Sharp's _Bicycles and Tricycles_ has a
formula. It allows you to calculate the stiffness of one side of the
hub. I've guesses a knock-down factor for the contribution of the other
side. Sharp and I both neglected any contribution by the rim's
stiffness.

At one point I calculated the linear "lag" (not sure what else to call
the effect of hub wind-up on the translational movememnt) due to a
torque I thought was reasonable. I don't remember what it was, but I
remember deciding that even a 12 spoke rear Shamal was more than stiff
enough torsionally.

Thanks for your reply, but did your analysis consider different spoke
patterns as well as spoke counts?

In particular, I'm interested in the paired-spoke pattern, radial,
1,2,3-cross.

J.

wrote in message
oups.com...
kevinkiller wrote:
Hi,

I'm wondering if anyone has done some kind of torsional wheel stiffness
study. That is how stiff the wheels are to resist the twisting that
hard
out of the saddle climbing puts on them.

I've seen and read about lateral wheel stiffness studies, where the
deflection of the rim along the hub axis is measured when applying
various
weights on the rim.

I'm considering a set of "aero" paired-spoke wheels and have been told
by
the manufactor that: "Although the spoke count is low, the paired spoke
configuration makes for a very stiff wheel" and I was wondering how true
this statement is in the sense of measured deflections in degrees per
foot-pount of torque for various rim depth/spoke configurations ... or
something like that.

Thanks,

J.

Torsional stiffness of the spoke complement can be calculated
approximately. Archibald Sharp's _Bicycles and Tricycles_ has a
formula. It allows you to calculate the stiffness of one side of the
hub. I've guesses a knock-down factor for the contribution of the other
side. Sharp and I both neglected any contribution by the rim's
stiffness.

At one point I calculated the linear "lag" (not sure what else to call
the effect of hub wind-up on the translational movememnt) due to a
torque I thought was reasonable. I don't remember what it was, but I
remember deciding that even a 12 spoke rear Shamal was more than stiff
enough torsionally.

kevinkiller wrote:

I'm considering a set of "aero" paired-spoke wheels and have been told by
the manufactor that: "Although the spoke count is low, the paired spoke
configuration makes for a very stiff wheel" and I was wondering how true
this statement is in the sense of measured deflections in degrees per
foot-pount of torque for various rim depth/spoke configurations ... or
something like that.

I think it may not have been measured because it is generally a very
small amount... and is probably easy to compute. I doubt that rim
stiffness even enters the equation. The # and thickness and elastic
modulus of the non-radial spokes, and the tangential distance from the
spokes to the hub center should be the important variables. You could
compute the force increase in the spokes for a torque applied to the
wheel, then the spoke length increase, and relate this to an angle of
rotation (a little geometry problem).

Maybe Dianne could produce the equation she used?

someone asked anonymously:

I'm wondering if anyone has done some kind of torsional wheel
stiffness study. That is how stiff the wheels are to resist the
twisting that hard out of the saddle climbing puts on them.

A typical wheel is analyzed in "the Bicycle Wheel" to show what effect
torque has on the spoke pattern. It shows that for a 36 spoke wheel
the loads are insignificant and far lower than the change in spoke
tension caused by rolling under rider load. What becomes apparent is
that all the spokes are involved, pulling and pushing the rim with
respect to the hub. Therefore, the average load on the rim is slight
and of course the spokes bing at about 1/3 their yield load, remain
unaffected.

Jobst Brandt

If you're looking for Wheel lateral stiffness, its been tested:

http://www.sheldonbrown.com/rinard/wheel/index.htm

What Jobst was trying to say is, that for the typical wheel you aren't
actually "winding up" the spokes.

Torsional stiffness is a non-issue for the typical wheel. If it's
tight enough not to collapse while riding, you can't wind it up with
the torque applied by even the strongest of riders.