AndyTea

I'm looking at two old Marin bikes to convert to electric bikes but i've not done a conversion before. What things make a bike a good base for a conversion?

AndyTea

Planning on making a mid-drive, 250W, 12-20ah battery conversion.

AndyTea

Probably with the Bafang conversion kits

Arrowana

68mm bottom bracket shell. The kits may say they are designed to work with both 68mm and 73mm, but actually installing one on a 73mm shell leaves almost no threads left for the lockring, so you have a higher chance of stripping the threads or having the whole thing loosen up. Not sure how applicable this is to models that aren't the Bafang BBS02.

A solid frame to serve as a base. Marins with hexagonal shaped tubing are more prone to failures at the bottom bracket, if the two you are looking at have hexagonal tubing, it might be worth seeing what other options are out there. On the other hand, 250w isn't that strong, so it's not like you are putting as much stress on the frame as a higher powered kit.

Most kits include brake levers designed for v-brakes and long pull disc brakes, so a bike that already has v-brakes or long pull disc brakes is a plus.

veganbikes

I would look for a frame that is designed to be an electric bike and can handle the loads going through it and the stress of having a very heavy weight of a mid drive motor and a battery on it. I would also look for something that can handle disc brakes so you can run a decent hydraulic disc brake so you can actually use a brake better designed for an e-bike.

2old

A lot depends on your intended application. However, steel mid 90's MTB's make excellent donor bikes IMO, and have the 68 mm BB referenced above. I've had eight trouble-free, maintenance-free (of the motor kit) years of off road riding on this hardtail MTB. Please ask any specific questions about your requirements.

Doc_Wui

All my bike conversions are ridden on pavement,. so I didn't have to worry about jumps and hard knocks of a battery on the frame. and never even considered the possibility that a mid motor could twist the BB out of the bottom of a diamond frame. I know that hub motors can rip out the drop-outs on forks and sometimes the rear frame but that is half worksmanship and half frame strength, Go with a steel frame if it worries you. I've got a 750W bafang on an aluminum frame diamondback, a 300W Tongsheng on a giant .alloy frame, and a second 300W Tongsheng on a an old steel 10 speed.

One area where I take more care is in the battery mount. I don't trust two ill positioned 5mm braze-ons to hold a battery that starts at 7 lbs. I'll add more attach points.

I think where people have issues is running 12 speed rear cassettes, wanting to spin 52T front chains, and trying toi fit a battery inside a frame that has a rear suspension spring.

2old

My son recently appropriated the hardtail MTB above and I built a full suspension (pictured below) with a circa 2006 Trek that had been used for pedal duty. The Blackburn "water bottle cage with Styrofoam protection houses the battery or a put a smaller one in a seat bag. I have a connector that can use both simultaneously.