2023 Surly Karate Monkey build with Bafang BBS02 750w mid-drive

[Snowcrow19]

This is my current build and the only thing I swapped out was the Shamano/SunTour 12-speed drive train with an Advent-X 10-speed cassette and 36T Lekkie bling ring. I had to grind away an area of the BBS02's gear casing to improve the chain line as much as possible. I'll be moving one of the smaller cogs to the back of the cassette to improve the chain line further. I've put 96 miles on it as is and have yet to have it drop the chain!

In range testing thus far with I have managed to put on 52.1 miles over 3 days, (no payload) with the 52v 21Ah battery still showing half charge! Not bad for the mountainous terrain of Vermont, the land of the continuous roller coaster! I included a few photos for context.

[73Eldo]

Cool build. Looks like a pretty decent sized battery, 21ah? 50 miles out of that seems pretty reasonable. One the voltage starts to drop it tends to go fast so I would not expect to get a ton more miles out of it but at least now you know you can easily plan for a 50 mile ride and leave some headroom for a little more speed or feeling a little more lazy if you want to.

I presume you are mostly riding on pavement or hardpack trails, not really off road? One reason I guess that is the range, offroad tends to eat power up faster and having that kind of weight up that high. Its not too bad till you start having to lean the bike at which point you really feel it.

Mine fit in the triangle but one time I bought a used pack and didn't want to trust it on a long ride so I put my old pack which wasn't as large as yours on my rack like that and made it like 7 miles into the ride at which point I had a situation where I had to pump on the pedals requiring a little side to side swinging of the bike and I just about lost it. When it started to happen I had no idea why but then figured it out. If I was stuck with a small triangle like that I think I would look at flatter packs down lower on the sides of the rack.

[Snowcrow19]

Yes, it is a 21Ah battery, and I guess I'm used to the weight being up high as my other build is a rack mount also. I do some pavement but usually travel the backcountry dirt roads and hard-packed single tracks. I'm in my late 60s adventure biking and technical riding is not for me! As you had said, it greatly limits your range. I'm sure there are still some improvements to make, but it's a start!

[Mike_V]

Nice eBike 'crow, and it looks like it will handle a little snow with your max traction set up soon enough in those mountains.
Well written, pictures and data ! OK and by tomorrow the fallen leaves from Hurricane Lee

[ncmired]

Hi Snowcrow19 - thanks for posting the build info and pictures, they always help.

[DCErik]

Tell me more about having to grind the motor case. I'm considering swapping my BikesDirect Gravity DeadEye frame for a KM on my BBSHD bike, but don't think I want to have to grind away the motor housing. Currently on a 42t Luna chainring and running an IGH on 135mm dropouts. Thanks!

[73Eldo]

The reason some of us grind the housing is to avoid having to use spacers. Spacers tend to push out the chain line. It does depend on what the chainstay does after the gear housing. If keeps kicking out after the gear case grinding won't help even with offset chainrings.

The Luna Eclipse 42 is about as offset as you can get so if you can place the motor so the chain ring teeth just barely clear the chainstay thats as good as it gets spacers or not. It would be of you stick it in with that combo and the gear case hits before the teeth do that maybe grinding could be an advantage.

[Retrorockit]

While playing around with the zip tie mod, which provokes chain drop. I came up with a chain guide that is working for me with a flat 50t chain ring on a BBSHD. It puts the chain onto the chainring at the top just like a derailleur does at the bottom. Full power in all gears and no short stacked cassette.
I started a thread about it, but no photos of the final version. they're stuck in my phone for some reason. I've posted other pics. recently. No idea what the problem is.

https://electricbike.com/forum/forum/main-forum/diy-discussion/164236-diy-bbshd-15t-chain-guide

[Snowcrow19]

Update

My "Pack Mule loaded with everything put food & water for a test run. Bafang 750w mid-drive powered by 52v 21ah and got ~60 miles range with an elevation gain of 3,941ft. The battery was at 12% SOC at the end of the test ride.

[Retrorockit]

That's an impressive range for a cargo bike situation. I get range anxiety if I try to go much more than 40 miles with 24Ah. 48V. Of course I'm usually bucking a stiff breeze off of the ocean. You must be providing a fair amount of the power yourself.

[Snowcrow19]

As part of my bikepacking kit, I included a wall charger and 100w solar blanket (aka security blanket) in one of the panniers. I would have made it home eventually! I had made the same trip a month earlier and unloaded with no issues so I was pretty confident in my calculations, but it doesn't hurt to be prepared! Yes, I think putting in some effort pedaling is part of the experience, how could you call it cycling otherwise?

[Retrorockit]

I pedal almost all of the time at any steady speed, but I can't keep up with the BBSHD when accelerating. So was this an overnight trip with solar charging during the day?
I bought a solar charging kit also. But it's a backup power source for hurricanes. I also got the inverter for powering stuff with bike batteries. I haven't taken it out of the box yet.