Gear selection and conversion for mid drive motor

AdrianKe

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I bought an old late 90s/ early 2000s Cannondale mountainbike to refurbish and convert to an ebike. The bike is stripped and I am taking everything apart and cleaning.
WhatsApp Image 2024-04-29 at 14.26.54_6ebb6a2e.jpg

The derailleur is a Shimano Deore XT and the gears is 3x9.

My idea is to use a bafang BBS02 and the PAS support will be capped at 25 km/h but I want to be able to pedal to a good 35 km/h before pedalling out. The bike will be a commuter.

I want to keep shifting minimal so were wondering if a 9 speed casette can be changed out to a 5 speed, if so, what will need to be replaced? (derailleur, shifters, casette, hub, chain, spacers)

I need to replace the shifter in anyway because I do not like the original grip-shift that operates in the opposite direction.
 
You might look to go to a 7 speed just to make finding the cassette you want easier and cheaper. If you are trying to prevent ghost pedaling at high speeds you will want your high gear to be an 11 tooth sprocket. I don't think you are going to find that in a 5 speed. Shimano Deore XT is a lovely derailleur, why lose it. I built a BBso2b from a 1998 Kona Munimula. Your worry will be where the rear derailleur cable runs and what the motor rests on. I would recommend you look at the Luna stabilizer bar to add to your set up. I used that bar and a stainless and rubber conduit strap bolted to the chain stay to hold the motor about 3/8" from the frame so it would be solid and not jam the derailleur cable. If you still feel the need to go all funky with this, there is a guy down under on YouTube called ToastyRides who renovates and converts all sorts of retro bikes to different configurations. It is worth watching. Good luck.
 
I converted an old mountain bike with a bbso2 and had the same rear derailleur cable setup and I just had to get a lower profile cable guide and it worked just fine. It probably wont be a problem but if it is get a lower profile guide like these.

I would also recommend a seven speed much more common for parts than fives, and your nine speed derailleur may or may not work but it's worth a shot.

 
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