Belt Drive Advice for a DIY E-Bike

Hope you guys are OK with a bike guy posting over here… :astonished: This site has been very helpful.

I added a hill assist to my Mountain Bike using a Turnigy D5035 125KV Motor (the orange one) and a VESC.
I’m driving the crank directly using #25 chain with 10:1 reduction (9T, 90T sprockets). 4S battery. It works great, but I’m curious to see if a belt drive might work as well and be a bit quieter.

I read a bunch of threads here with lots of good information, but not quite what I’m looking for. I would really appreciate any advice/suggestions on design guides, sources for pulleys & belts (off the shelf and custom…), and any general thoughts.

Here are the design parameters: At least 10:1 reduction ratio 450 Watts at 60 RPM Cadence, which works out to about 175 lb belt tension. (May be able to reduce watts/tension just a bit…) 7.2" max pulley diameter .575" large pulley width, so 1/2" wide belt (Maybe 15mm with large effort) Dust for sure, and possibly dirt. Up to .010" radial runout on the large pulley Prefer not to use an idler/tensioner, or crazy high tension

My initial feeling is that this is a difficult application for a belt. However, you guys seem to be able to make belts work in difficult conditions. Thanks!

I dont think a belt could handle the strain put on it if youre using it for a bike :o

you could always try gear over belt if you still want to use the motors you have now :man_shrugging:

I can only hear the belt skipping as you use the breaks, unless you apply it too gently to be used efficiently

maybe HTD5 isnt the type of belt for you? maybe find some more sturdy belts…?

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How long of a chain are you running?

@Sn4Pz is correct. Going belt you would have slippage, ripping and tearing of belts.

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I don’t know if this helps, but no motor braking here. The motor just turns the cranks, not the rear wheel.

Also, I’m only using 4S, and will never see over 35 amps, or 500 watts.


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The chain is about 32 inches, but I have a few inches of adjustment…

Try shortening it. Not tight shorten though.

You’re always going to have noise from chains though. You can reduce it but its metal against metal lol.

I just think the length, as well as wheel size, rider weight and speed are probably working against you in this case, belts likely wont work here :frowning:

at least HTD5, maybe find a different type of belt? something automotive?

Yup, and the 9 tooth motor sprocket doesn’t help…

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watch tom stantons YouTube video on his diy ebike it’s a great series

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or something motorcycle, but an HTD5M would work fine if it was at minimum 20mm wide i would think.


I think you might have a chance at 20mm but I think the size of the wheel is just too much for it :thinking: Not to mention if it was cold, they would snap like taffy

or if they get wet they might stretch.

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