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I have a Gates carbon belt drive on a NuVinci hub.

I haven't bothered with the the whole tensioning using the app and everything, but I have a set-up where it is perfectly quiet and I've never had it skip. But the belt feels quite loose.

My question is whether there is any benefit to higher belt tension apart from preventing skipping? It seems the belt does not stretch and too high a tension causes all sorts of problems like bearing strain, noises etc.

So is the ideal tension then the tension that's just high enough to prevent skipping but no higher? Or is there some benefit I can't think of tensioning past that point which is what the app/tools etc. attempt to do?

Thanks in advance!

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  • I don't have a belt, but my understanding is that belts run at a higher tension to extend the effective life of the belt, not for preventing skipping.
    – Criggie ♦
    Oct 26, 2018 at 3:35

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Don't have a belt drive myself, but a guess would be: Running appropriately snug (I assume they crafted the app for a reason) would make sure that the stresses and load on the belt is distributed appropriately. Consistent tension on the belt has to be better than a looser belt undergoing stress fluctuations as portions of the belt change from a loaded state (on/between the rear hub and the front crank) to an unloaded state. I expect that higher stress fluctuations on a looser belt would create additional 'belt fatigue' and reduce the belt life.

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    Hmm. Interesting. On the one hand I can see how tension variability may shorten belt life. On the other though I can't see how pre-tensioning reduces tension variability. Say you pre tension to P newtons. I then step hard enough on the pedals to generate T newtons of force in the belt. The top half of the belt will be carrying P+T newtons of tension, The bottom half will carry just P. The difference between the two is T, which is not a function of P. So I don't see how pre-tensioning helps in this way.
    – s445203
    Oct 27, 2018 at 11:29
  • Hmm, could less snugness allow for tooth (nub? whatever the bumps on the belt are called) engagement "higher" on the tooth, which might increase shear forces, if that makes sense. I can picture it in my head, but spelling it out is escaping me at the moment.
    – railsdog
    Oct 28, 2018 at 19:19
  • Perhaps an additional benefit of 'enough' tension will be that load is more evenly distributed between multiple belt and cog teeth. If you picture a belt which is 'on' but has no pre-load / tension then unless tolerances are very tight then only a single tooth will be carrying any load at a time (under high enough pedalling load that tooth would elastically deflect enough to start sharing the load with its neighbours). By having 'enough' pre-load multiple teeth will already be in this state of sharing load.
    – kabdulla
    Oct 28, 2022 at 19:14

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