Has anyone got real world Rohloff and Gates belt drive experience and could you please help me out?

In the new year I’m looking into buying a new 29er+ bike frame which is capable of fitting a Rohloff hub with a gates belt drive and I’m rubbish at maths.

When reading through the Gates website from page 38 http://www.koga-signature.com/docs/Gates-Rohloff-Manual_English.pdf my brain has melted.

I want to run the 29er+ for bivi riding in the hills, so low gearing is important but looking here http://www.carbondrivesystems.com/products/cdxsprockets at the pulley/cog sizes here I can’t work out which would be the best Rolhoff set up for a 29er+ wheel diameter.

There are only 3 sizes of Gates CDX rear sprockets for the Rolhoff hub a 19, 20 and 22 tooth/pulley rear sprockets.

So, what size would I need up front to help with climbing on the bigger wheels?

Also with an EBB what size chain ring could I go up to on the front as an option if I wanted to fit it for faster flatter rides but using the same belt and rear pulley?

Thanks you all you mtb maths experts.

Gearing is a very personal thing – what’s a low gear for one person might be too high for another. If you want to play with gear ratios, I have free software:

K-Gear Software

Best thing to do, especially if your mind doesn’t work in gear inches is to put in your existing gear ratios to start with, to work out what you have – then you can play about with the Gates sprockets.

And having a quick play with the ratios I have on my Rohloff (44/16 on 26″), if you have a 29er with a 50t on the front, a 20 or even a 22 would be about right – 22 would give you lower gears of course.

Silly question time…..

Does a Gates chain ring size equate to the size of a normal chain ring?
i.e. the front rings seem quite big, does a 50 tooth Gate ring mean the same as a 50 tooth conventional ring?
http://www.carbondrivesystems.com/products/cdxsprockets

What frame are you considering, sounds very interesting?

Remember a 29+ wheel has quite a bit bigger circumference than a 29er wheel so as previously suggested working out gear inches and comparing to what you currently find comfortable would be a good indicator of what to go for.

Does a Gates chain ring size equate to the size of a normal chain ring?

No. But what matters is the ratio of front cog to back cog, so as long as you compare the ratios you’re fine.

bencooper – Member
Does a Gates chain ring size equate to the size of a normal chain ring?

No. But what matters is the ratio of front cog to back cog, so as long as you compare the ratios you’re fine

Cheers Ben but what do I need to add into that great gear calculator

I’ve just worked out that a 50 (TOOTH) x 20 (TOOTH) would be a fraction lower at each end at my standard 3 x 9 combo.

But if you say that the Tooth to Pulley ratio isn’t the same what do I put in there for the belt drive to give me the same on a 794mm diameter wheel?
My 3 x 9 is 44-32-22 with a 32 x 11 on the back with a 740mm wheel diameter.

Cheers

If you’re using my gear calculator, then just bung the Gates pulley size in both. So 50×20 sounds right for you too, giving similar ratios to the setup I have.

The only thing you can’t do is say “a 44t chainwheel works for me, so a 44t Gates pulley will give the same gearing”.

Looking at the frame I’m after the biggest Gates Pulley is a 46 in size.

Does anyone know what standard cog tooth size this would be the same as to help with the calculations on Ben’s calculator?

Just bung in 46 as the chainwheel size. Then the size you pick at the back will be the rear pulley size.