Originally Posted by
Kimmo
Regarding whether a wheel stands or hangs, what about Brandt's measurements? No detectable increase in tension of any spokes in a loaded wheel, only a decrease in tension in the bottom spokes. If you accept that as fact, how can you possibly say it hangs?
IMO this counterintuitive conclusion serves to illustrate that most of us fail to understand just how clever this tensegrity structure is, almost entirely failing to appreciate that the tension is a structural component.
I'd be interested to see if Brandt's results would be mirrored in the tensions of leading and trailing spokes in a torqued wheel... No increase in tension of trailing spokes would thoroughly confirm Brandt's view, although I'm not sure the opposite would necessarily invalidate it.
Anyway, I reckon it's pretty safe to say that it's a lot more complicated than many folks imagine. A wheel stands on its lower spokes in the sense that these are the only ones experiencing a change in tension. Go figure.
I've measured spoke tensions when a bike is stationary, with a rider weight on the saddle, and without a rider.
When the rider is seated, the spokes at the very bottom lose some tension, the 1, or 2 spokes right next to the contact patch (at both sides) gain just a little tension.
When a torque is applied (front brake locked to keep the bike in place, while a pedal is pushed by the rider's whole weight), I have measured trailing spokes gain tension.
Both of these measurements align with the way Jobst describes the load transfers in his book. At least the way I understood it.
The reason for my experiment was Jobst's claim that the rear wheel left-hand side spokes don't take almost any driving torque. My assumption was that modern hubs might be a bit stiffer, and just might allow the left-hand side spokes to take the driving torque.
Bottom spokes are loaded in compression, but the way for a spoked wheel to take such load is by having all the spokes in tension, and then the compressive load is taken by a decrease in tension, because a spoke can't take compressive force without any tension - it would buckle.