- Joined
- Feb 20, 2013
- Messages
- 869
- Location
- Axedale, Victoria, Australia
- Website
- axerail.coffeecup.com
I needed to see how easy or difficult it was going to be to fit a second chainring to a Bafang BB01 e-Assist conversion. As eLectricks was not going to have any cassette on the rear wheel, I needed to be sure that low end gearing was going to be adequate. The best way of doing this would be to fit a “mountain climbing” chainring to the front – if that was indeed possible.
Steep uphill can be a bit of a grind when not using the motor due to only have the single chainring, as even lowest gear can be too high. Think about not being able to access the two smaller chainrings on you current ride and you’ll get the idea. The single chainring is held on by five hex-drive studs – hex cap bolts as they are called by my supplier. Of course, their mounting radius does not match any of the five-stud or five-spoke chainrings that I have in my collection. The radius is actually smaller on the Bafang.
I found a 28t chainring with an axially offset centre and with five holes that could possibly be used for mounting. It had an offset centre and it fitted very neatly between the spokes of the Bafang chainring. I needed to space it from the existing chainring for chain clearance. A steel disc with five stud holes at the small radius of the Bafang chainring, and another five stud holes at the radius of the additional chainring, could allow the two chainrings to be used. The additional chainring could be bolted to the steel disc. Spacers would be required to accommodate the offset of the additional chainring, and the whole could be attached to the drive motor by longer mounting studs. This was something that I just had to try.
The right-hand-side pedal was removed, allowing removal of the existing chainring. A disc was made and drilled as required, using both chainrings as templates for the stud holes and the large central clearance hole. The additional chainring was bolted to the disc. Three spacer discs (stacked), required to fill the void created by the added chainring’s offset, were cut from a small sheet of discarded aluminium. Their outer circumferences were contoured to clear the heads of the added chainring mounting bolts. Then they were cut radially in half to avoid having to cut the large central clearance hole in each one. If I had to do them again, I would try and use a single piece of aluminium and make other arrangements to cut the large centre hole instead of fiddling with six individual pieces. Five longer studs were purchased to bolt the whole assembly to the Bafang drive motor. The complete process took far longer than I had anticipated.
A brief test proved the concept with the lowest gear selected all round showing a very low bottom gear. Owing to more slack chain takeup requirement, the front chain guard had to be shortened and two links had to be removed from the chain. Any uphill grade that cannot be ridden with this setup would be ridiculous and should be circumnavigated.
The addition of a front derailleur, with a friction shifter, would complete the modification. Funny, that was three months ago and the derailleur has not yet been fitted. Ironically, having gone through these gymnastics, I discovered that Amazon carry a wide range of chainrings for Bafang drives. All that should be required to use these chainrings is a spacer and longer mounting studs.
Steep uphill can be a bit of a grind when not using the motor due to only have the single chainring, as even lowest gear can be too high. Think about not being able to access the two smaller chainrings on you current ride and you’ll get the idea. The single chainring is held on by five hex-drive studs – hex cap bolts as they are called by my supplier. Of course, their mounting radius does not match any of the five-stud or five-spoke chainrings that I have in my collection. The radius is actually smaller on the Bafang.
I found a 28t chainring with an axially offset centre and with five holes that could possibly be used for mounting. It had an offset centre and it fitted very neatly between the spokes of the Bafang chainring. I needed to space it from the existing chainring for chain clearance. A steel disc with five stud holes at the small radius of the Bafang chainring, and another five stud holes at the radius of the additional chainring, could allow the two chainrings to be used. The additional chainring could be bolted to the steel disc. Spacers would be required to accommodate the offset of the additional chainring, and the whole could be attached to the drive motor by longer mounting studs. This was something that I just had to try.
The right-hand-side pedal was removed, allowing removal of the existing chainring. A disc was made and drilled as required, using both chainrings as templates for the stud holes and the large central clearance hole. The additional chainring was bolted to the disc. Three spacer discs (stacked), required to fill the void created by the added chainring’s offset, were cut from a small sheet of discarded aluminium. Their outer circumferences were contoured to clear the heads of the added chainring mounting bolts. Then they were cut radially in half to avoid having to cut the large central clearance hole in each one. If I had to do them again, I would try and use a single piece of aluminium and make other arrangements to cut the large centre hole instead of fiddling with six individual pieces. Five longer studs were purchased to bolt the whole assembly to the Bafang drive motor. The complete process took far longer than I had anticipated.
A brief test proved the concept with the lowest gear selected all round showing a very low bottom gear. Owing to more slack chain takeup requirement, the front chain guard had to be shortened and two links had to be removed from the chain. Any uphill grade that cannot be ridden with this setup would be ridiculous and should be circumnavigated.
The addition of a front derailleur, with a friction shifter, would complete the modification. Funny, that was three months ago and the derailleur has not yet been fitted. Ironically, having gone through these gymnastics, I discovered that Amazon carry a wide range of chainrings for Bafang drives. All that should be required to use these chainrings is a spacer and longer mounting studs.