This is a chain-drive bike with the Nexus hub. Is it possible to convert to a mid-drive? I realize the chain needs to remain parallel to the frame and a friend who has built a few ebikes for himself says it won't work for this bike. He says I need a measurement of very near 51 mm from mid-frame to the chain ring and my bike measures 44 mm. Don't the conversion-kit makers have chain rings to adapt to bikes such as mine? Or is there another reason why a mid-mount motor can't be used with the setup?
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I just ended up buying a 7 speed shifter off Amazon with cable already attached. That will get me by for now. Ill probably replace the rear casset next just gotta figure out which one to get. Thanks for all the help and replies.
I have a Shimano nexus 8 specific for e-bikes combined with a tong-sheng 750 watt torque sensing motor. The Surly build has travelled 200 miles and counting with my new hub. From what I've read (and I know Shimano tries to conservatively cover their butt) the extra torque of a mid-motor is problematic and can strip the internal gears of most nexus / alfine hubs with more than 5 gears. If you have a nexus 3 speed you should be okay. Same with the 5 speed.
I purchased a Nexus E-Bike 8 speed Hub ( SG-C6001-8 ) from England that is e-bike rated, (it wasn't available from the States). Note the e-bike safe IGH stock number has a "1" at the end SG-C6001. Not to be confused with not e-bike specific hub SG-C600 !!!
What is below is advice for 6 speed and up IGH's.
Now a mid drive like tong-sheng 750 watt is less powerful than a Bafang 750 watt, it's a smaller motor and the tong-sheng will deliver power proportional to how hard you pedal, hence "torque-sensing." The harder you push down on your pedals the more power the Tong-Shang mid-drive puts out. There are 4 levels of pedal assist you can set the motor to, with only a bit of help at the lowest level, and quite a bit at the highest level of pedal assist. (No "pedal pressure sensing" with the Bafang)
As you probably know to stop pedaling when you shift with a internal gear hub (IGH) as an any mistakes can strip the hub = I was very, very hesitant to combine a Bafang with a Nexus or Alfine 8 speed, as those Nexus / Alfine gear hubs are fragile compared to a derailleur--even the e-bike Nexus SG6001 isn't rated for 750 watts. And Bafang will deliver those 750 watts not too subtly, moreover all at once. I wouldn't use a Bafang mid-drive with a Shimano Nexus 7 or 8 speed. You're okay with many 3 or, 5 speed hubs. That's the main piece of advice.
Check out Johnny N.O.'s video on his personal Benno cargo-bike with a Sturmney Archer 5 speed IGH and a Bafang 750 watt mid-motor. He will give the sterling advice that only he can give.
If you have an e-bike rated internal gear hub to combine with a mid mount motor--(only a tong-sheng or 300 watt mid-motor or less for above 5 speeds) I would take into account,
1. Your weight,
2. The amount of hills you climb,
3. The lag-time to stop pedaling to when you shift so the IGH remains safe (there is a free-wheel in the chain-ring when you stop pedaling that keeps the chain moving for a brief second after ceasing to pedal with a mid-mount motor) , Note that the Tong-Sheng has no speed-shift sensor configured to their motors.
4. And finally, perhaps most importantly, Setting the motor to lower pedal assist modes to save the IGH from too much torque.
And weigh it out further from there. I, myself wouldn't use a Bafang for the purpose of powering any affordable IGH 6 speed and up----Though I love my other e-bike, a cargo e-bike with a Bafang BBS02 to death--it has the traditional, safer derailleur-- IMHO the Bafang would've torn up a Nexus 7 or 8 for sure, even their "e-bike 8 speed IGH".
Final caveat, is that the motor I use, the Tong-Sheng torque sensing mid-drive has a reputation for being less reliable than the Bafang. I have already had to crack it open and replace a controller. Be aware that there isn't much in the way of do-it-yourself videos for that task of inevitable repairs.--But if you're mechanically inclined, you should be okay with a Tong-Sheng.
Can't get this forum to accept a photo. What you would see is a line drawn from the center of the seat post at the level of the top of the chain ring to the top of the chain ring. I'm told that measurement, in order to use a mid-mounted motor, should be very close to 51 mm. The measurement on my bike is 44 mm. If there were a dish-shaped chain ring of the right size, it could align the chain with the rear sprocket. The dish shape would need to compensate for the 7 mm difference between my bike and the ideal (51 mm) measurement so that the chain remained parallel to the frame.
not sure, theres no pics to see what youre referring to. we promote mid drive motors here and to avoid hub motors / premade ebikes altogether