W K said:"David Damerell" <[email hidden]> wrote in message
Quoted message said:W K said:>>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".]
Quoted message said: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.
Quoted message said: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 hidden]> Kill the tomato!
