Re: Wheel-less tire question

On 3/13/2025 11:29 AM, bp@www.zefox.net wrote:

This is mostly a philosophical question, but maybe it has a technical answer.
 The rim of a bike wheel is a relatively heavy component, largely because
of its circumference. Could it be dispensed with, at least in the case of
a tubular tire, by making the spokes extensions of the tire carcass cords?
The hub would remain mostly the same, with the "spoke" cords of the tire
laced around anchors on the hub flanges.
 It wouldn't be very convenient to handle, indeed, a spider's nightmare.
But, it could fold up much like a parachute. The tire would have to be
inflated to a pressure sufficient to support the needed spoke tension,
which might be rather higher than the pressure used in traditional
tubular tires.
 It would be hard to manufacture, getting all the spoke lengths matched
to run true being the most obvious difficulty. But intuition suggests
it would be about the lightest construction possible, as well as the
most compact when stowed before use.
 Another way of asking the same question is to ask the stiffness of a
fully-inflated, unmounted tubular tire compared to a traditional wood
or metal wheel rim.
 I've never handled one and so have difficulty guessing.
 Thanks for reading, and any insights.
 bob prohaska
     

Short answer = no.
A tensioned wheel, (as bicycles wheels with actual tensioned spokes, not including carbon sheets) has to have a noncompressible* rim of constant* circumference in order to not flop around.  It's an elegant thing, with among the highest strength to weight ratios of human built structures.
The principles are similar to an arch:
https://tse2.mm.bing.net/th?id=OIP.OtdqiBPMvo3_wmobAocS0AHaEN&pid=15.1&w=474&h=274&c=7
Tension inward on the spoke is compressing the rim circumference making a rigid structure. Vertical load on an arch (keystone) is supported by the sides, with load along a vector (not vertical as a post and lintel). An arch made of cooked gnocchi would of course fall apart, as would a bicycle wheel with a fabric 'rim'.
Pressed steel auto wheels are different, in that there is not a tension component. The face behaves like an infinite series of compression spokes (as wooden wheels use) and as such is heavier for any given strength.
Further to all that:
https://www.astounding.org.uk/ian/wheel/
*practically but not absolutely
--
Andrew Muzi
am@yellowjersey.org
Open every day since 1 April, 1971