4 ms·
The rolling resistance data is interesting, but it would be nice to see some more realistic testing. For example ramping the pressure up on a smooth surface giv
by Neil44 2y ago
The rolling resistance data is interesting, but it would be nice to see some more realistic testing. For example ramping the pressure up on a smooth surface gives lower rolling resistance on a rolling road. But in the real world super high pressures cause the whole bike and your body to shudder and vibrate, which also consumes energy. So there is a sweet spot, between heating the tyre up too much, and passing too much vibration through.
- tpm 2y agoThe question is whether more realistic testing is really needed. At some speed below 30km/h aero drag takes over and at higher speeds that's basically the only thing that matters. Unless you are riding steep hills in which case total weight is the thing that matters.
- Neil44 2y agoExcelent point. Personally I think I would rather run a few PSI less and have confortable ride.
- londons_explore 2y agocan't you also get a smoother ride by having slightly slacker spokes on wheels? Then the wheel rim bounces over every rock and pebble, but the axle doesn't.
- tpm 2y agoOr even very slack spokes, like the Berd (UHMWPE) ones, but then power transmission is slightly less efficient.
- _Wintermute 2y agoNot really, spokes work under tension rather than compression, you're essentially hanging from the top-most spokes on the wheel. Also if your spokes are too slack, they can move in the hub, cause wear, and are likely to snap at the elbow.
- londons_explore 2y agookay - slightly stretchier spokes.
- wiredfool 2y agoNo. Wheels are a prestressed linear superposition of overall tension and a compressive load at the bottom. Generally, you'll see ~4 spokes at the bottom of the wheel relaxing to take the vertical load. (in a properly built wheel) This is due to rims not being completely rigid, but being a somewhat flexible beam. Rims are nowhere near rigid enough to do the "hang from the top" thing. Spokes will break at the elbow, but generally due to fatigue, which is made much worse when there are stress reversals. Fatigue is when cyclic loads cause small imperfections to grow into cracks, and eventually failure. If you have stress reversals under rolling loads (where the stress goes from tension to compression, anywhere in the spoke elbow) you should expect to see spike failures in ~1000 miles. A stress reversal doesn't necessarily mean that a spoke is slack, because there are some interesting stress patterns in the elbow in poorly built wheels.
- _Wintermute 2y agoThe compressive load is negligible, that's why you can build a wheel entirely out of non-rigid spokes such as liteweight wheels or https://berdspokes.com/ https://berdspokes.com/
- wiredfool 2y agoThere should never be a _net_ compressive load on a spoke, but a spoke can carry a compressive varying/live load if there's sufficient pre-tension from the building process. You wouldn't want berd spokes to go slack any more than you'd want steel spokes to go slack.
- wiredfool 2y agoNo, you can't, because the elasticity of the spoke doesn't depend on the tension, only the cross section of the spoke. (and count of spokes, and to a lesser extent the lacing pattern).