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If I'd convert my drivetrain from a chain-based drivetrain into a belt-based drivetrain and I'd want to keep the exact same transmission, how do I know the required number of teeth for the front belt ring and rear cog?

E.g. I have a 44 teeth sprocket in the front and a 16 teeth rear cog. What would be the corresponding numbers of teeth in a belt-based drivetrain?

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    It is not just the ratio - its also what belt lengths are available. You haven't mentioned how this frame will tension the belt - there are no "tensioners" like a chain could have. The frame will require either trackends instead of dropouts, or an eccentric bottom bracket that can be rotated. You will require a belt length that matches your chosen cogs and has the correct total length for your frame. AND if your frame is a common diamond-frame design, it needs a cutout to get the belt into the frame - belts generally don't have a join.
    – Criggie
    Oct 16, 2022 at 8:11
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    Hi Criggie. I am eying at at a Veer split belt. veercycle.com/products/split-belt-pro
    – Stücke
    Oct 22, 2022 at 10:52
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    There are also tensioners for belts. See e.g. here blog.gatescarbondrive.com/2021/09/08/…
    – Stücke
    Oct 22, 2022 at 10:53

2 Answers 2

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You just need the same tooth ratio. The fact that it’s a belt drive with a different tooth size/shape doesn’t change anything about it.

There will be some size/availability constraints (since you can’t make the cogs arbitrarily small or big. Edit: and you also can’t get the belt in arbitrary lengths). The front cog teeth count shouldn’t be a whole integer multiple of the rear cog teeth to even out wear on the rear cog. For example 40t in front and 20t (ratio of 2) in the back is bad.

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  • Not sure where the cog wear thing comes from - I know fixed gear bikes like to have uncommon divisors, to spread out the number of wear/skid patches on the rear tyre (2:1 would give exactly 2 skid patches) Is it related to the pressure of the downstroke always being in the same place on the rear cog?
    – Criggie
    Oct 16, 2022 at 2:19
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    @Criggie: Yeah, I’m not too sure how bad it really is. On the front cog you can’t avoid it and it’s still lasting a long time.
    – Michael
    Oct 16, 2022 at 6:32
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    @Criggie It is indeed a result of the downstroke always being in the same places on the rear cog. My understanding though is that the problem is not the rear cog itself, but the fact that the asymmetric wear there has a bigger impact on the belt wearing out than if it were symmetrical, with this being compounded by the smaller size (and therefore tighter bend in the belt) of the cog as compared to the front. Oct 16, 2022 at 12:41
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Some completely identical ratios:

  • 11 teeth in front, 4 in back
  • 22 teeth in front, 8 in back
  • 33 teeth in front, 12 in back
  • 44 teeth in front, 16 in back
  • 55 teeth in front, 20 in back
  • 66 teeth in front, 24 in back
  • 77 teeth in front, 28 in back
  • 88 teeth in front, 32 in back

I'm not sure how small the Gates drive teeth are, but I'm sure you are able to find some reasonable number from this list.

It's also possible to slightly change the ratio, so little that you won't notice it.

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    Thank you for your response! However, I don't understand how this answers my question.
    – Stücke
    Oct 15, 2022 at 13:51
  • Got it. Sorry for being slow and thanks to @jusist!
    – Stücke
    Oct 16, 2022 at 9:06

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