W K <
[email protected]> wrote:
>"David Damerell" <
[email protected]> wrote in message
>>W K <
[email protected]> wrote:
>>>>>above, some less so "rim rigidity makes no difference", "spokes are never broken by drive
>>>>>torque"
>>>>Nope because drive torqs a very small fraction of spok load hub flange
>>He does, but he looks like a 13 yo who's _read_ The Bicycle Wheel. Doubling or even tripling drive
>>torque would still leave it a fraction of spoke load.
>If you are talking about bad pedalling styles and low gears you can make it very much higher than
>doubling or tripling.
[what about tandems, asks "W K".]
>Would you like to quote the actual calculations? Or do I have to line his pockets just to disagree?
Well, the Book says that typical spoke tension in a 36 spoke wheel is
1000N.
How much can a single rider push? Let's imagine a 70kg rider can put his whole weight on the pedal -
not actually pulling up on the bars, but still riding very hard, presumably out of the saddle. This
will exert a force of 700N 170mm from the BB spindle; about 120 Nm of torque.
1001/34 is a very low gear, increasing this to about 170Nm at the rear hub. Also, the Book tells us
that a typical rear axle transmits about 20% of the torque to the non-drive side; so we should
consider the (clearly greater) tension change in the right-hand side spokes. 80% of this torque
is about 135Nm - a typical hub flange might be about 30mm radius, so this would exert 4500N on
the spokes; however, it acts on 18 spokes (since as we know we can regard the pushing spokes as
being compressed by this load) for a tension change in each one of 250N. This would be 1/4 of
the spoke tension in the case where the wheel is undished and spoke tension is not higher on
the right-hand side; and I must reiterate that this is in an extremely low gear.
[Disclaimer; this is a bit back of the envelope, and I'm willing to have obvious errors pointed out
to me. It assumes a tangentially spoked wheel, I think. :-]
However, the Book also recommends large-flange hubs for tandems ridden vigorously, because then
torque may become a high proportion of spoke tension... so actually when you ask about "2 nonskinny
people on a tandem", Brandt does take that into account; your characterisation of him is unfair.
>No, he actually says that if you ride through glass you get a puncture and its as simple as
>that. Aparantly he would never dream of riding with 4mm thick rubber, which probably makes most
>the difference. He certainly hasn't commuted through the post industrial wasteland on an
>everyday basis.
In return, would you mind Googling up an article of his to justify this assertion about
what he says?
--
David Damerell <
[email protected]> Kill the tomato!
