Aero, Spoke counts, and tension..What's needed? [Archive]

Ken Lehner

05-06-2005, 07:54 AM

Aero, Tension, and Low Spoke Counts Oh My!!

It gets a little technical at points but these guys have a good handle on it.

www.barbarianbikeblog.blogspot.com

William

This one says all you need to know, and cuts through the bull****:

"A long time lurker, but I wanted to comment regarding wheels.

1. Spokes should **NEVER** break unless it is from a manufacturing
defect.
Manufacturing defects are rare and any spoke that is defective will break
either during the initial build or within the first few days of use.
Spokes that
break after this time do so because they are not stress relieved. There
are residual stresses at the elbows of the spokes that are caused by
the manufacturing process. If you don't relieve these stresses, then
eventually the spoke will break. I weigh over 200 pounds, often
commute with as much as 80 pounds on my bike, and have not had
a broken spoke not due to an accident as far back as I can remember,
at least 10-15 years, and I've never heard of a spoke breaking in any
of the 30-50 wheelsets I've built in that time either. Proper stress
relieving
results in a strong wheel which doesn't go out of true nor break spokes.

2. The weight of the wheel is inconsequential. If you take a bike, put
it in the largest gear (say a 53X12), and flip it upside down, you can
likely spin the rear wheel up to 40 MPH with one full crank revolution
from using just your arm. If you ride this bicycle and try to accelerate
it up to 40 MPH, you might never make it. The first example shows
the amount of power necessary to accelerate the wheel. The second
example shows the amount of power necessary to accelerate the
bike/rider combo. In relation to the mass and power necessary to
accelerate the complete bike/rider combo, wheel weight is basically
inconsequential. Aerodynamic effects outweigh weight in all but steady,
steep climbing. As a real life example, look at match sprinters, who
rely on acceleration the most of all bicycle racing events. They will
always use a heavy but aerodynamic wheelset.

3. In general, wheels that don't go out of true when a spoke breaks
aren't
built with enough tension. The amount of tension you can put into the
spokes greatly determines the load carrying and impact handling
capacity of a wheel, so whether you build for a 100 pound cyclist or
a 200 pound cyclist, you should use the same tension.

4. Harshness from certain wheelsets because they are "stiff" is not
backed up by measurement. Radial stiffness of most wheelsets is in
the 5000 lb/inch to 15000 lb/inch range. A 200 pound load on the ends
of this spectrum result in rim deflections of 0.04 inches in the least
stiff wheel to 0.013 inches in the stiffest wheel. Meanwhile, between the
tires and saddle, the amount of deflection is magnitudes greater,
probably on the order of a half inch or so, which is 12.5 times greater
than the least stiff wheel. It is hard to imagine that a rider could feel
something that offers that little contribution. It is likely that
wheelsets
which are described as "stiff" may sound differently or transmit
different frequencies of vibration, and these may be interpreted as
harsh.

Thanks for all the information on your list.

Wayne Lim"