Well, that didn’t go as well as I had hoped. I tested a few different PAS levels (0-4). I had set the controller to 9 levels, so didn’t go beyond 4 because I was having some other technical issues. What I learned with this mid-drive Bafang motor is that the PAS level effects the power output for both the pedals and throttle. I think this is a good design, but just takes some getting used to. Also, the optional shift sensor works great to reduce power from the motor during shifting. This also is a great feature and should significantly improve drive line wear.
The problem I’m having though is the chain jumps off the front chainring when shifting into the top 3 high gears (smallest outer gears). I’m running a 9-speed cassette and I’m convinced that the chain angle between these gears and the chainring is such that the chain simply cannot track on the chainring so it pops off. But what to do?
- add spacers to the Bafang motor so it lines up better with the rear cassette – this is a lot of effort and it might not work
- replace the default chainring with one that doesn’t go in so close to the chain stay – I need to research this option to see what’s available, and it still might not work
- replace the rear cassette and shifter, and maybe the chainring too for better alignment – besides, who really needs 9 gears on the rear cluster anyway? – more research required
- go with a single speed rear gear, or something that has a lot better alignment with the chainring – this would put a lot more load on the motor on PA hills – not a good idea
- adjust chain tension via the rear derailleur by changing derailleur angle and/or removing chain links – need to explore this option, but will hold off until I decide what to do about the chainring
- do nothing – they say this is always an option – I would adjust the derailleur so it can’t go down to the 3 highest (smallest) gears – doable but not optimal
Other than the chain jumping the chainring, I think I’m going to like this mid-drive system once I get used to it. A little more tinkering and I think I’ll have this sorted out. In the meanwhile, my rear-hub e-bike rocks and I have enjoyed all 500 miles I put on it since building it last year…
**Update**
I opted for the ‘buckshot’ approach versus the scientific method, meaning I’m changing a bunch of things at the same time to sort out my chain derailment problem, including:
- new 7-speed 12-28 tooth cassette and 7-speed shifter – this change also lets me use my motor-cut-out brake lever on the rear brake
- new e-bike rated KMC chain
- new 44 tooth Aluminium BBSHD Chainring – 186mm diameter & 7mm offset – this replaces a 46 tooth chainring with a 19mm offset. In theory (if the offset is measured the way I think it is) this would move the chainring 12mm further away from the chainstay (original chainring has a 19mm offset and chain derails off the outside of the chainring in the 3 high gears with a 9-speed cassette).
Word has it that the standard steel chainring that comes with the BBSHD motor is ‘junk’, so it’s likely that just changing out the chainring with a higher quality one would have fixed the problem.
My next update will report just how well these changes worked to fix my problem. Stay tuned…