Hi, I am trying to get a custom frame built for a Bafang M510 or M560. I'm designing this bike for many purposes, including remote touring, mountain biking, and commuting. My goal is to have as wide a range of gearing as reasonably possible. The bike should be comfortable to ride with no motor power. And even with my current 0.63 low gear, I want even lower.
I've considered a few options. On my current normal bike, I have recently swapped out the 3x9 drivetrain with a 3x10 using the Sturmey Archer CS-RK3 IGH, 36t chainring, and 11-43t Linkglide cassette. This gives a nice range, but chainline is not quite right (which is exacerbated by Linkglide), and the amount I have to pedal to engage the hub is excessive, which is very noticeable when mountain biking.
My plan had been to get a frame built with 135mm dropout spacing so I could fit this hub and an 11-50t Linkglide cassette. But 11spd Linkglide is likely incompatible or dangerously close to incompatible with a 135mm wheel because of spoke clearance, and chainline is a big concern. Bafang specifies the chainline for M510 to be 53mm. I have not measured my current chainline, but my bottom bracket is advertised for 50mm with a 3x crankset. My chainline is already too far out, so I would expect this to be horrible with an M510 without an offset chainring, offset spider, and/or mounting the chainring to the wrong side of the spider. And as far as I know, the Bafang motors have their own discrete engagement points, making the combination with the IGH too slack for my liking.
I've considered a Rohloff (or even the discontinued Kindernay XIV), which support 142/148mm spacing, but engagement points are still a concern with Rohloff in low gears, and I still want more gear range regardless. For Rohloff, it looks like the only way to achieve more gear range with a mid-drive motor would be with a 2x/3x crankset. I would much prefer to deal with some of the drawbacks of multiple chainrings on a mid-drive if it means I will always have the gearing I desire.
This brings me to my hopeful solution. My preference would be a conventional and durable hub like a DT Swiss 350, a wide-range cassette, and two or three chainrings. My preference is chainrings is uncommon on mid-drives, but I've seen it on production bikes like some from Yamaha or on DIYs like the TSDZ2. I'd prefer 3x, because my current middle gear is pretty good for most riding without having to constantly switch into another like I think I'd have to with 2x.
My plan would be an 11-45t Linkglide cassette, a CUES RD-U8020 rear derailleur with 48t capacity, and as wide a range front setup as possible (and just hope Shimano is generous with their capacity spec and/or just deal with a slack chain if in small-small.
The main challenge to this plan is hopefully not chainline (if I go with a 142mm or 148mm hub) but rather getting a compatible spider. For 11-45t, I'd like to have my smallest chainring be 22t or 24t. This would require a 58/64/74 BCD mount. For a big chainring, 42/44/46t would be ideal. And an ideal middle chanring would be 36t. Most spiders available for the M510 or similar motors are 104 BCD and designed for only 1 chainring. For 2x, I'd do 26t and maybe 40t for the large. Getting more range without exceeding derailleur capacity too much is easier with 3x than 2x.
Both Yamaha and Bosch have 104/64 BCD spiders available. The only 2x spider I found with Bafang spline is this one from FSA, but it is only 110 BCD. I would think it'd be possible to mount two chainrings (one on either side) of a 1x spider and just hope the spacing is about right. Some useful items I've found is a "triplizer" chainring from Interloc suggested here for 74/110 BCD (though I would prefer steel over aluminum, and it is discontinued), a similar chainring from Thorn for 130/74 BCD, and a spider adapter called Avid Microdaptor (also discontinued) to mount a 58 BCD charinring on 74 BCD (this option would allow me to mount 22t on 74 BCD. So it remains that I have not found an available solution for Bafang for mounting a sub-104 BCD chainring.
Does anyone know of a non-jank way (spider-only or spider + easy-to-find adapter(s)) to mount 2x or 3x chainrings on a Bafang mid-drive? A 104/64 BCD (or even 110/74) spider for Bafang would be nice. Or any alternative suggestions for ultra-wide gearing with Bafang?
I've considered a few options. On my current normal bike, I have recently swapped out the 3x9 drivetrain with a 3x10 using the Sturmey Archer CS-RK3 IGH, 36t chainring, and 11-43t Linkglide cassette. This gives a nice range, but chainline is not quite right (which is exacerbated by Linkglide), and the amount I have to pedal to engage the hub is excessive, which is very noticeable when mountain biking.
My plan had been to get a frame built with 135mm dropout spacing so I could fit this hub and an 11-50t Linkglide cassette. But 11spd Linkglide is likely incompatible or dangerously close to incompatible with a 135mm wheel because of spoke clearance, and chainline is a big concern. Bafang specifies the chainline for M510 to be 53mm. I have not measured my current chainline, but my bottom bracket is advertised for 50mm with a 3x crankset. My chainline is already too far out, so I would expect this to be horrible with an M510 without an offset chainring, offset spider, and/or mounting the chainring to the wrong side of the spider. And as far as I know, the Bafang motors have their own discrete engagement points, making the combination with the IGH too slack for my liking.
I've considered a Rohloff (or even the discontinued Kindernay XIV), which support 142/148mm spacing, but engagement points are still a concern with Rohloff in low gears, and I still want more gear range regardless. For Rohloff, it looks like the only way to achieve more gear range with a mid-drive motor would be with a 2x/3x crankset. I would much prefer to deal with some of the drawbacks of multiple chainrings on a mid-drive if it means I will always have the gearing I desire.
This brings me to my hopeful solution. My preference would be a conventional and durable hub like a DT Swiss 350, a wide-range cassette, and two or three chainrings. My preference is chainrings is uncommon on mid-drives, but I've seen it on production bikes like some from Yamaha or on DIYs like the TSDZ2. I'd prefer 3x, because my current middle gear is pretty good for most riding without having to constantly switch into another like I think I'd have to with 2x.
My plan would be an 11-45t Linkglide cassette, a CUES RD-U8020 rear derailleur with 48t capacity, and as wide a range front setup as possible (and just hope Shimano is generous with their capacity spec and/or just deal with a slack chain if in small-small.
The main challenge to this plan is hopefully not chainline (if I go with a 142mm or 148mm hub) but rather getting a compatible spider. For 11-45t, I'd like to have my smallest chainring be 22t or 24t. This would require a 58/64/74 BCD mount. For a big chainring, 42/44/46t would be ideal. And an ideal middle chanring would be 36t. Most spiders available for the M510 or similar motors are 104 BCD and designed for only 1 chainring. For 2x, I'd do 26t and maybe 40t for the large. Getting more range without exceeding derailleur capacity too much is easier with 3x than 2x.
Both Yamaha and Bosch have 104/64 BCD spiders available. The only 2x spider I found with Bafang spline is this one from FSA, but it is only 110 BCD. I would think it'd be possible to mount two chainrings (one on either side) of a 1x spider and just hope the spacing is about right. Some useful items I've found is a "triplizer" chainring from Interloc suggested here for 74/110 BCD (though I would prefer steel over aluminum, and it is discontinued), a similar chainring from Thorn for 130/74 BCD, and a spider adapter called Avid Microdaptor (also discontinued) to mount a 58 BCD charinring on 74 BCD (this option would allow me to mount 22t on 74 BCD. So it remains that I have not found an available solution for Bafang for mounting a sub-104 BCD chainring.
Does anyone know of a non-jank way (spider-only or spider + easy-to-find adapter(s)) to mount 2x or 3x chainrings on a Bafang mid-drive? A 104/64 BCD (or even 110/74) spider for Bafang would be nice. Or any alternative suggestions for ultra-wide gearing with Bafang?
