was looking around a not too local bike shop today and wondered what this
little cog is all about ( Pros and Cons )

It’s wrapped around the pivot point so there should be no chain growth as the suspension moves. Should keep it more supple all the time. Some normal bikes utilise this chain growth to stiffen things up so it tightens up under power. I suppose this is less useful a feature with a motor to help and you’ll be putting power down all over the place and you don’t want it randomly stiffening

Commencal Supreme DH had similar, although they seem to have moved back to a more conventional setup now.

To achieve a similar effect to having the pivot in-line with the chain ring.

Nothing that complicated on the ebike. It is just there because the “chainring” is so small the chain wouldn’t clear the chain stay in the highest gears.

it wouldnt clear the swingarm

beaten to it edit

If it was just to clear the chainstay then it could have been put in a number of places. They also could have shaped the chainstay differently as its a custom frame. It’s very deliberately bang on the pivot so I suspect there is more to it.

On the topic of “could have shaped the chainstay differently”, why isn’t it a straight line between the rear axle and the pivot?

Thanks Nickjb for the explanation sound sense

is it better or worse or just another way of doing the suss bit .

why isn’t it a straight line between the rear axle and the pivot?

To more closely match the other side? Some Specialized Enduro’s had different pivot points on the left and right sides and I could never get my head round it!

The other side is wrong in the same way, and it can’t be just for the sake of rear brake routing, they have a massive loop of cable hanging underneath the BB.

It could be structural, either:

A – avoiding a long straight stay which may be quite weak
B – avoiding a sharp curve close to the pivot

I’d say it’s creating a virtual chainring size. It’s a very small sprocket on the cranks – looks like an 18-tooth. The extra cog takes it back to being the same as a 32T….maybe.

I remember when there was a lot of discussion about pedalling-induced bob. Maybe it’s there to stop that, with the chainring being so small.

I’d say it’s creating a virtual chainring size. It’s a very small sprocket on the cranks – looks like an 18-tooth. The extra cog takes it back to being the same as a 32T….maybe.

Are you thinking it changes the gearing? It has absolutely no affect on the gearing.

But with that size chainring it must spin out at about 10mph! The chainwrap is also tiny.

Is there some kind of internal gearing? https://www.bosch-ebike.com/en/ebike-systems/performance-line-cx/

But with that size chainring it must spin out at about 10mph! The chainwrap is also tiny.

It is geared inside so the chainring goes round more than once for every time the cranks go round.

You lot are all over thinking this, it is just to get the chain to stop rubbing on the chain stay… Used by a few manufacturers who use the Bosch motors with tiny chainrings.

^ was just looking to see that. So the crank is not coupled directly to the chainring and spins faster than the crank? weird.

Doesn’t help with the answer but interesting website regardless for demonstrating that it doesn’t affect the gear ratio.

Gear Sketch

The new Commencal still has a chain idler.

Shaped chainstays are for tyre and chairing clearance

OP – you need the snipping tool in your life (it literally changed mine!) 😆

It’s probably on the pivot point to use the same mounting point, so cheaper.