Rohloff Speed 14 hub gearbox with Bafang BBS mid-motor

[chain]

Hey Andre ...what happened with this build ?

This:

Bombing down the hill at Kilbrogan

I'd love more info as i want to do a similar rohloff build and need info re alternate chainrings/chainline etc . PLEEEEEZ update!
thanks
bill in exeter

The idiot software of this board just lost my complete description of the installation and use of a Bafang BBS midmotor with a Rohloff hub gearbox because it claimed it was over 10K words. What sort of a motherless programmer writes a deadend loss like that with no return path?

I don't have time to rewrite all of that for five people to read, Bill, so I'll just answer your specific questions and in future place my complete review someplace safer.

***
Bill "need(s) info re alternate chainrings/chainline etc"

The Rohloff chainline demanded by Bernd Rohloff is within 1mm of 54mm, measured from the centreline of the hub (on a well-built from from the centreline of the seat tube!) to the longitundinal centreline of the teeth on the chainring, i.e. to the middle of a roller on the chain if it doesn't fit too loosely.

The offset of a standard dished chaingring for the Bafang BBS mid-motor is 51mm. I used 3.5mm total of spacers, as 2.5mm and 1mm, mainly because I already had them and they were already painted bike color, between the bottom bracket shell and the rear ride of the motor supposed to rest on the bottom bracket shell's rim. This moved the chainline to within 0.5mm of the desired chainline.

Practical measurement is from the far (non-driveside) of the seat tube to the centre of the thickness of the teeth, minus half the diameter of the seat tube.

Spacers you can buy from Chainreactioncycles.com, which is where I got mine, as either dedicated bottom bracket spacers or, if you can determine that they have the same inner and outer diameter as your bottom bracket shell, as cheaper and often generic sprocket spacers.

I don't know what "etc" is. If you have a specific question, ask here and I'll try to answer. Good luck with your build, Bill.

 

[chain]

The next problem is the tooth count of the chainring. The motor is wide, so the chainring is dished to fit over it and give a tread (the trendies and poseurs call it the "Q factor" so they can express surprise when you don't know what it is -- it's the width over the outside faces of the cranks where the pedals screw in) within reason; roadies like the tread to be as narrow as possible

The dishing, with the size of the motor, limits the tooth count. The smallest chainring from Bafang, last I heard, is 44T. Smallest available in the aftermarket, last time I looked, was 42T, pricey but beautiful, carved from solid aluminium in Italy. If you like the 38x16 Rohloff gearing that a lot of tourers have followed me into, tough. I like steel chainrings, so I fitted Bafang's own 44T dished ring, for two further reasons, one already described above: it's an easy fit and fix for a hyper-correct Rohloff chainline.

The other reason is more esoteric. Because I ride in street clothes and don't like trousers clips, and have anyway developed a near zero-maintenance bike, I use a Hebie Chainglider on my everyday bike. The Chainglider must use the special Rohloff rear end, and the Chainglider front ends that work with the Rohloff rear end are limited in tooth counts, coinciding with the Bafang tooth counts only at 44. So I could fit that one or go custom... Maybe later I will have a custom ring machined out of stainless, because I had good experience with the 38T Surly stainless ring, maybe I'll stick with the Bafang pressed steel chainring. We'll see. The point is, the Bafang 44T got me going almost instantly, without waiting for custom work. Nor did it, with the torque of the motor, seem a hard choice after being accustomed to the soft option of 38x16; motor just filled in. And, of course, with 14 evenly-spaced gears in the Rolloff, it wasn't ever going to be as big a problem as at first I feared. Wonderful what we discover with 20-20% hindsight.

Before the Chainglider-compaitble chainring arrived from China, I tried riding in street clothes without chain pretection. I didn't get very far before my trousers were twice caught up in the chainring and chain. I gave it up as recipe for broken bones.

 

[willywombat]

you're a star Andre ..sorry about the 10,000 word loss ...totally ridiculous
if you find a copy or redo let me know pls.
I recently bought a surly Ogre for the build and have one problem with the chainline . As it has a 73mm bb rather than 68, it is still possible to fit a bafang but as you have less threads only one lockring can be used so i'm told ( + some locking compound for security. Because of this it seems that i wouldn't have any room to fit your suggested 3.5mm spacers on the drive side to improve chainline with the speedhub. TBH though I find it difficult to believe that a speedhub wouldn't run just fine even if the chainring is 4mm out . By the time the chain reaches the hub sprocket the angle difference won't be much .
may be wrong though and perhaps a poor chainline could stress the hub internals ?
I havent seen a bafang unit in the flesh but could you not space the chainring rather than the bottom bracket ?
Bill

 

[chain]

you're a star Andre ..sorry about the 10,000 word loss ...totally ridiculous
if you find a copy or redo let me know pls.
I recently bought a surly Ogre for the build and have one problem with the chainline . As it has a 73mm bb rather than 68, it is still possible to fit a bafang but as you have less threads only one lockring can be used so i'm told ( + some locking compound for security. Because of this it seems that i wouldn't have any room to fit your suggested 3.5mm spacers on the drive side to improve chainline with the speedhub. TBH though I find it difficult to believe that a speedhub wouldn't run just fine even if the chainring is 4mm out . By the time the chain reaches the hub sprocket the angle difference won't be much .
may be wrong though and perhaps a poor chainline could stress the hub internals ?
I havent seen a bafang unit in the flesh but could you not space the chainring rather than the bottom bracket ?
Bill

Hang on a moment, Bill. If you're fitting a Rohloff gearbox to the installation you describe, with a 73mm bottom bracket, then you want zero (0mm) in spacers. In fact, you will have 2mm too far in spacers. I don't think it will matter all that much, and you can't do anything about it anyway, but you don't want to aggravate the distance by adding to it unnecessarily.

 

[willywombat]

good point doh! 73mm - 68 =5mm .........5/2= 2.5 so 2.5 further to the right than standard = chainline of 53.5 ....

 

[chain]

good point doh! 73mm - 68 =5mm .........5/2= 2.5 so 2.5 further to the right than standard = chainline of 53.5 ....

A chainline of 53.5mm, I think, spot-on. You won't get it closer than that!