Trevor said:Mark McMaster wrote in message <[email hidden]>...
Quoted message said:For well designed and constructed wheels, the spoke breakage
rate should be minimal. The expectation should be that a
wheel should be able to have several worn out rims replaced
without a spoke breakage (several of the wheels I have built
are on their second rims with all the original spokes).
I tend to agree with this posting, but know your methods differ to mine.
You do not mention wheel or rim stability, is it of no concern to you?
James Starley illustrates his high wheeler with 40 spokes paired together at
the rim.
A safety bikes wheel is half this size so 20 spokes should be sufficient for
a 27" rim.
Due to non pairing I think 30% less ie 14 spokes may be sufficient.
I think you are making a number of assumptions. Firstly,
Starley's wire spoked wheels were an innovation to make an
improvement on wooden compression spoked wheels, which are
by their nature very heavy. In addition, since the single
row of spokes in wooden compression spoke wheels have no
bracing angle, the spokes must be very broad (and heavy) to
achieve the desired lateral stiffness. Starley's spokes
were at a fairly wide bracing angle, even for today's
smaller wheels, so they were likely able to achieve the same
(or greater) lateral stiffness at less weight.
We also don't know the weight and stiffness of his rim,
which are also important in achieve wheel strength and
stiffness. There are a number of modern 700c wheels which
have a reduced number of spokes - 20, 16, 14 or even 12
spokes. However, for these wheels to to adequately stiff and
strong, they need a stiff and strong rim. Using a larger
number of spokes allows one to use a much lighter rim, with
the resulting wheel being both lighter overall (despite
their greater number of spokes), and more reliable, for the
same strength and stiffness.
Quoted message said:Extract from 3959 Starley patent of 1874 "...increase their stability &
improve their speed. " He mentions strength, lightness and beauty of
appearance. "The spokes are screwed up until the heads of the spokes bear
lightly against the rim. This arrangement I follow for the spokes of both
flanges, and I thus produce a crossing of the spokes which will posses an
elegant appearance, while at the same time I secure great stiffness with the
use of a light wire."
Why should stability not be an issue 130 years later? The point was a
light wheel could be constructed that was stable. His 'crossing of the
spokes' was directed at the flange which was pierced with a drill'd and
threaded pin into which a spoke came from opposing points of the wheel and
not the interleave as used today.
Here you are making your largest assumption - how do we know
a patented idea really has all the benefits that are
claimed? Patent examiners don't make quantitative analyses
of claims, they simply verify the inventions are
non-obviousness, unique and might have some utility. You
should probably know that only a small fraction of
inventions that are patented actually make it to market,
most often because they are either impractical, or do not
offer enough of an improvement over existing designs (if
they offer any improvement at all). Not to mention the fact
that patent examiners are not always as thorough as they
could be, and patents are frequently discovered to be
invalid in later investigation. For example, Rolf Deitrich
managed to get issued a patent on pairing spokes in bicycle
wheels, despite the fact that some of the first wire spoked
wheels over 135 years ago had paired spokes!
Another major assumption is that Starley had optimized his
wheels on the first go-around 130 years ago. Since the
actual mechanics of how loads are distributed (and how the
stiffness of each component effects the load distribution)
in tension spokes wheels were still not known until many
years later, it is likely that Starley's wheels were not yet
optimized, and were heavier than they needed to be to
achieve the required strength and stiffness. Just how stiff
and light were Starley's wheels? While some versions might
have been as stiff as today's wheels, they were probably
much, much heavier. If you are building your wheels based
on a 125 year old patent, it is highly likely that your
wheels are also far from optimized.
Mark McMaster
[email hidden]
