Reliable Drivetrain For Bafang Ultra powered MTBs

[bram.biesiekierski]

Hi.

So im having some trouble with my Bafang Ultra powered e22 drivetrain. The problem is the chain skipping over the teeth on the cassette under load. The top half of the gear range all do it to some extent now. With some gears almost un-rideable with motor assistance. The cassette teeth now have visible damage/wear. The teeth are rolling over on the load side. I've put less than 50km on the bike from new, and have already trashed this cassette after about 40km.

The combo is :
Chainring - Praxxis Steel E-Ring 36t. (Brand new)
Chain - Shimano XT 12 speed. (Brand new)
Cassette - e13 Helix 12 speed. (Used, approx 500Km)
Rear mech - Sram GX Eagle. (Used, high Km)
Shifter - Sram GX Eagle. (Used, high Km)

I used the 12sp drivetrain when i built the bike, because I already had most of the components in my spares box. The e13 Helix cassette is aluminium for the 2 lowest gears, and steel for the 10 highest gears. I figured the steel part of the e13 cassette would be tough and long lasting. Boy was I wrong. It must be made from very low grade steel, as it has worn so heavily in such a short time.

Now I have the dilemma of what to do moving forward. I can purchase the individual parts of the e13 Helix cassette seperately. So I can replace the worn steel section. But this won't stop it from happening again in another 40km.

I am concerned that perhaps the derailer is worn out, and not keeping enough chain tension on the drivetrain.

I think the best solution is to get a new complete drivetrain groupset. But I dont know what to get. I want something that will take the power from the motor. I don't need as many gears as it has now. With the motor assistance, I find I probably only need half as many, and I wouldn't need such a large range either. And something that won't break the bank would be nice aswell.

 

[Zimmerframe]

There could be a combination of factors which may not of helped.

Derailleur adjustment with the b screw could bed limiting wrap around, so inviting more early wear on the cassette.

Using a pre worn cassette with the new chain. It may already have been semi worn depending how/where you ride, how you clean/lube, how you change gears. A new chain on a word cassette will just wear the cassette even faster (depending how worn the cassette is).

Riding style. A lot of people who are new to emtb think they can change gear under power. Yes, you can yo a degree, but it takes time to learn how much and how long to back off before you change gear and how to reapply the power once you change. For most this just becomes second nature, for some they still slam through the gears under full load and just destroy their cassettes.

Yes, the 12 speed Shimano cassette does say you can shift under load. But there's still a degree of sympathy needed and that's on a bike without a motor.

None of that's saying it's what you do. The cassette maybe second hand. There could be many other factors or a combination of some of the above.

A general consensus is that something like a 10 speed setup is more than adequate for most emtb use, which is cheaper and stronger. Though a Shimano 12 speed if looked after and ridden correctly can still give you thousands of Kms of life.

 

[bram.biesiekierski]

I did have the B screw come loose on my second ride. Once I noticed, I correctly adjusted it using the plastic Sram guide tool. I'm wondering if the damage happened at that point. And now that it is damaged, it's just skips constantly.

I did learn pretty quickly not to shift under load with the bike. The shifts are brutal. Like flatshifting a sequential race box. Except, the bike drivetrain isn't as tough.

The e13 cassette is my own, I pulled it off my other bike when i built the e22 up. It had maybe 500kms on it, if that.

 

[bram.biesiekierski]

Does anyone have any thoughts/opinions on the Shimano Linkglide range? It's thier eBike specific 10/11spd offering. And it's pretty reasonably priced for a complete group.

I've been quoted about AUD $300 for the 10spd, and AUD $450 for the 11spd. But there are some delays with availability.

I've also seen that Sram has thier EX1 range, which is decently priced, except for the cassete, which is quite expensive. Anyone have used the Sram EX1?

Lastly. Has anyone heard of "box prime" drivetrains. They are supposedly eBike rated wide-range 9spds. Very cheap. Complete #2 and #3 groups for under AUD $250.

Im a bit of a Sram fan. But I will consider others if they are reliable enough for the Bafang Ultra.

I'd prefer XD driver freehub compatibility. But I do have a Shimano HG freehub for this wheel, and I can purchase Shimano Microspline freehubs if needed aswell.

 

[bram.biesiekierski]

So I've pulled the pin on the Box Prime 9spd drivetrain ecosystem. I can buy 2 complete groups for the same price as just replacing the e13 half cassette. So I did.

I figured these things are so cheap, that having spares is probably a good idea. Better than waiting a week for replacement parts if i do have any more mechanical issues. I ordered a Box Prime level 2 group, and a Box Prime level 3 group. Both 9spd. (Level 1 being the most expensive, and level 4 being the cheapest)

The level 3 ebike version has a 12-50 cassette, and a single click shifter.

The level 2 also is an ebike friendly kit, it comes with 11-50 cassette and a multi click shifter. (They put a caveat that your not recommended to use a multi click shifter for ebike use.)

I will probably initially use the 12-50 cassette, the level 2 chain and derailer, and the single click shifter.

The 12-50 will loose gear range compared to the 9-50 12spd setup. (417% vs 556%) But that is ok if I gain reliability. As it was with the 9-50 cassette, and 36t chainring, I never use the lowest gears. And also never really use the highest gears except on paved surfaces.

Im also going to use the enormous standard bafang Chain ring with this combo. I think this is potentially alot of what my problem is. Using a smaller 36t chainring is like using a larger lever. It's a force multiplication.

I think of it like a lever, where one side the lever is the motor, with its rated 160nm of torque. The fulcrum is the crank rotation axis. And the other side of the lever is the chainring. The smaller the diameter (radius) the more force exerted on the chain. This is amplified by the fact that smaller diameter has less teeth in contact with the chain. So more force, going through less number of teeth.

The Bafang 44t chainring will force me to naturally use lower cassette gearing to achieve any similar given ratio. This will spread the force over more teeth, and hopefully improve reliability. But also probably keep the chain line more off center, as I will be using more of the lower gears. A benefit of this will be that the derailer is going to be wound further over against its spring. Hopefully also keeping a higher tension on the chain.

Even with the huge bafang 44t chainring. My top gear max speed will actually reduce with the 12-50 cassette. (36÷9=4 vs 44÷12=3.67) but this is OK, if I gain reliability. As I said. I didnt often use the top gear of the 9-50/36t combo. Except on pavement.

 

[twistgripper]

Some discussion about EX1 here Shimano, we have a problem. - EMTB Forums

 

[Ford Prefect]

On our m620 powered ebike, I've been riding on the SRAM NX, 11-speed shifter with a 42tooth-to-11tooth cassette & 40tooth front chainring. (All standard issue; 2021 Frey AM1000 v5.)

Although I am contending with enormous quantities of extremely sticky & abrasive grime due to deplorable conditions in the city, & have accidentally inflicted a few heavy "chunk" gearshifts under load, I found no noticeable tooth wear whatsoever after 420 miles.

My observations about this layout:

• The spline shaft sensor, used to measure pedal torque on the m620, maxes out around 60Kg. This is typical of most pedal-assist torque sensors, but feels like very little effort for me. I would love to replace this sensor with one reading up to 120Kg; m620 motor controllers configurable via standard UART serial connection protocol, can be calibrated for this... provided one has such a sensor available. (Anyone???)
• The earliest two gears are only useful when I am making a very steep climb.
• No matter how I adjust it (even had it to a couple shops), there are always one or two gears which don't retain as well as the rest; usually they're a middling gear, so I avoid using that gear & then give the cable tensioner knob a twist tighter or looser if I really need that gear for a while. (Every derailleur I've ever had with more than 7 speeds, exhibited this to some extent. I would welcome the precision & speed of a wired electronic shifter...)
• Medium assist (max ~550W) feels like plenty, at any speed below 15 MPH.
• Even at zero assist, I feel no need for so many low gears.
• I double shift constantly, because I don't need the gear ratios in between.
• Cadence feels very high, at any speeds above 24 MPH; to the point where I can't load the pedals while rolling downhill. (Applying drive force to the rear wheel lends stability through a turn, so it's nice to always have a harder gear available.)
• On challenging technical bike routes, this gearing works great. In addition, I'll note that the peak output is entirely unneeded until some combination of heavy cargo or rider laziness and extreme steepness, converge.
• On automotive routes where traffic constantly tries to go >35 in 25MPH zones, it would take at least 2KW of power to really "keep up", regardless of gearing. (Anyone dreaming of >45MPH emotorcycle speeds should seek out at least 3KW output... aaaand 12KWh capacity, if they plan to ride long at those highway speeds.)
•  A lower cadence would allow my legs to contribute something (anywhere from 100W "casual" effort to >750W peak effort) instead of the diddly-squat pedal force that's achievable once cadence shoots past 120.

Personally, for this same shifter, I would prefer a 46tooth chainring pulling a 48tooth-to-11tooth cassette. The wider shift range would retain nearly the same starting gear ratio while reducing cadence in later gears.

Having a more manageable cadence, at which I can exert close to my peak output, would not only affect top speed (which I care about only in special circumstances), being able to exert greater pedal force at moderate speeds would improve range, too.

I am about 6'10" & 250 pounds; my weight on the front pedal can easily exceed the torque rating of many commonly recommended components. The m620 on the Frey draws up to 1440W at max output, but I almost never exceed 1100W (more often ~550W hill climbs) & spend most time at less than 25% output. Smaller riders have no need of the >1KW until they're carrying cargo or approaching top speeds.

On flat ground with no wind, top speed on motor alone is right around 28.2 MPH, & pedaling barely helps because the cadence is too high. With moderate assist & pedaling like mad I can make it to about 32 MPH; the same top speed I've clocked on my manual 3×10 speed MTB.

Max output doesn't accomplish much additional top speed, because none of us who've ridden it could apply any pedal force at such high cadence; another 400 Watts of motor power doesn't help much when it means losing all power from one's legs.

I constantly shift two gears at a time, because even with the ebike off I just don't need such closely-similar gear spacing; a change in ratio of 20% or more, would be just fine. My 3×10 bike has a perfect gear ratio for any speed within its range, but in practice I only use that precision to maximize efficiency during long slow climbs on the smallest front chainring; at all other speeds, I use the middle or top chainring & still find myself double shifting for expediency until some noticeable pedal force is required.

Any time the ebike is actually on (even at 7% output), 11 gears feels like overkill for only a 400ish percent shift of gear ratio.

I would love to try the Nine from 3x3:
A 9-speed hub shifter rated for 250Nm of torque, with gear ratios stretching from 1.901 to 0.346, for a shift range of 554%. Available with twist, click, or electronic controls. Compatible with disc brakes & either chain or belt drive. 3x3 says it weighs 2Kg, & has less than 6% drag.

Judging by specs, the Nine seems like the very best shift system commercially available, for an m620 based ebike?

 

[bram.biesiekierski]

I

On our m620 powered ebike, I've been riding on the SRAM NX, 11-speed shifter with a 42tooth-to-11tooth cassette & 40tooth front chainring. (All standard issue; 2021 Frey AM1000 v5.)

Although I am contending with enormous quantities of extremely sticky & abrasive grime due to deplorable conditions in the city, & have accidentally inflicted a few heavy "chunk" gearshifts under load, I found no noticeable tooth wear whatsoever after 420 miles.

My observations about this layout:

• The spline shaft sensor, used to measure pedal torque on the m620, maxes out around 60Kg. This is typical of most pedal-assist torque sensors, but feels like very little effort for me. I would love to replace this sensor with one reading up to 120Kg; m620 motor controllers configurable via standard UART serial connection protocol, can be calibrated for this... provided one has such a sensor available. (Anyone???)
• The earliest two gears are only useful when I am making a very steep climb.
• No matter how I adjust it (even had it to a couple shops), there are always one or two gears which don't retain as well as the rest; usually they're a middling gear, so I avoid using that gear & then give the cable tensioner knob a twist tighter or looser if I really need that gear for a while. (Every derailleur I've ever had with more than 7 speeds, exhibited this to some extent. I would welcome the precision & speed of a wired electronic shifter...)
• Medium assist (max ~550W) feels like plenty, at any speed below 15 MPH.
• Even at zero assist, I feel no need for so many low gears.
• I double shift constantly, because I don't need the gear ratios in between.
• Cadence feels very high, at any speeds above 24 MPH; to the point where I can't load the pedals while rolling downhill. (Applying drive force to the rear wheel lends stability through a turn, so it's nice to always have a harder gear available.)
• On challenging technical bike routes, this gearing works great. In addition, I'll note that the peak output is entirely unneeded until some combination of heavy cargo or rider laziness and extreme steepness, converge.
• On automotive routes where traffic constantly tries to go >35 in 25MPH zones, it would take at least 2KW of power to really "keep up", regardless of gearing. (Anyone dreaming of >45MPH emotorcycle speeds should seek out at least 3KW output... aaaand 12KWh capacity, if they plan to ride long at those highway speeds.)
•  A lower cadence would allow my legs to contribute something (anywhere from 100W "casual" effort to >750W peak effort) instead of the diddly-squat pedal force that's achievable once cadence shoots past 120.

Personally, for this same shifter, I would prefer a 46tooth chainring pulling a 48tooth-to-11tooth cassette. The wider shift range would retain nearly the same starting gear ratio while reducing cadence in later gears.

Having a more manageable cadence, at which I can exert close to my peak output, would not only affect top speed (which I care about only in special circumstances), being able to exert greater pedal force at moderate speeds would improve range, too.

I am about 6'10" & 250 pounds; my weight on the front pedal can easily exceed the torque rating of many commonly recommended components. The m620 on the Frey draws up to 1440W at max output, but I almost never exceed 1100W (more often ~550W hill climbs) & spend most time at less than 25% output. Smaller riders have no need of the >1KW until they're carrying cargo or approaching top speeds.

On flat ground with no wind, top speed on motor alone is right around 28.2 MPH, & pedaling barely helps because the cadence is too high. With moderate assist & pedaling like mad I can make it to about 32 MPH; the same top speed I've clocked on my manual 3×10 speed MTB.

Max output doesn't accomplish much additional top speed, because none of us who've ridden it could apply any pedal force at such high cadence; another 400 Watts of motor power doesn't help much when it means losing all power from one's legs.

I constantly shift two gears at a time, because even with the ebike off I just don't need such closely-similar gear spacing; a change in ratio of 20% or more, would be just fine. My 3×10 bike has a perfect gear ratio for any speed within its range, but in practice I only use that precision to maximize efficiency during long slow climbs on the smallest front chainring; at all other speeds, I use the middle or top chainring & still find myself double shifting for expediency until some noticeable pedal force is required.

Any time the ebike is actually on (even at 7% output), 11 gears feels like overkill for only a 400ish percent shift of gear ratio.

I would love to try the Nine from 3x3:
A 9-speed hub shifter rated for 250Nm of torque, with gear ratios stretching from 1.901 to 0.346, for a shift range of 554%. Available with twist, click, or electronic controls. Compatible with disc brakes & either chain or belt drive. 3x3 says it weighs 2Kg, & has less than 6% drag.

Judging by specs, the Nine seems like the very best shift system commercially available, for an m620 based ebike?

It sounds like you could really benefit from a larger front chain ring. I have said it many times on here, that these motors are really well suited with larger front chainrings.

The problem with the NX group not ever being able to get all gears lined up can be a couple of issues.
Firstly, the NX uses shimano HG freehub interface. And these style of interface have big problems because each individual gear on the cassette is keyed directly to the freehub splines. And with such small area to distribute the load, and the fact these freehub parts are exclusively made of aluminium, it means they very commonly wear into the freehub and rotate as the do.

The other really big problem with NX is in the derailer. The small chain wheels have a plain sleeve as a bearing. (Higher models use a different design) Which has excessive side to side play from new, and only gets worse with use. This side to side play means it's extremely difficult and sometimes just impossible to correctly index the shifting, so all gears are happy. Although, if you still have problem with different derailers, then it's not that.

Yes, I aslo agree that close ratio jumps are not a good match for these motors. I started with 12spd, then went down to 9spd, and I now have a 7spd kindernay IGH. It's has issues, but I do really like the wide spacing of the gears.

I was wanting a 3x3, bit they were not available at the time I needed an IGH. So I settled for kindernay. It's not great, and I am having shifting issues. But so far it does what I needed it to do.

 

[Ddc6284]

I

It sounds like you could really benefit from a larger front chain ring. I have said it many times on here, that these motors are really well suited with larger front chainrings.

The problem with the NX group not ever being able to get all gears lined up can be a couple of issues.
Firstly, the NX uses shimano HG freehub interface. And these style of interface have big problems because each individual gear on the cassette is keyed directly to the freehub splines. And with such small area to distribute the load, and the fact these freehub parts are exclusively made of aluminium, it means they very commonly wear into the freehub and rotate as the do.

The other really big problem with NX is in the derailer. The small chain wheels have a plain sleeve as a bearing. (Higher models use a different design) Which has excessive side to side play from new, and only gets worse with use. This side to side play means it's extremely difficult and sometimes just impossible to correctly index the shifting, so all gears are happy. Although, if you still have problem with different derailers, then it's not that.

Yes, I aslo agree that close ratio jumps are not a good match for these motors. I started with 12spd, then went down to 9spd, and I now have a 7spd kindernay IGH. It's has issues, but I do really like the wide spacing of the gears.

I was wanting a 3x3, bit they were not available at the time I needed an IGH. So I settled for kindernay. It's not great, and I am having shifting issues. But so far it does what I needed it to do.

I have appox 2500 miles on my Ultra. Ex1, is great because you can just the 3 smallest cogs if and when needed. I would suggest a 42t or 44t ring. The Ultra likes to spin. So I would stay away from the large chainrings.
When I first got mine. I was going through cassette fast. Make sure your not in the two lowest gears when climbing hills or taking off from a start. Would also suggest getting a program cable. There's a lot better tunes than running stock. Just my two cents. Dave

 

[bram.biesiekierski]

I have appox 2500 miles on my Ultra. Ex1, is great because you can just the 3 smallest cogs if and when needed. I would suggest a 42t or 44t ring. The Ultra likes to spin. So I would stay away from the large chainrings.
When I first got mine. I was going through cassette fast. Make sure your not in the two lowest gears when climbing hills or taking off from a start. Would also suggest getting a program cable. There's a lot better tunes than running stock. Just my two cents. Dave

I now use a kindernay vii. Which has outlasted the 2 different cassette systems ive used. But it has been an absolute nightmare aswell in its own regard.

The kindernay shift hydraulics are just pure shit in every regard. Trying to keep them bled up properly is like trying to keep water in a bucket with a hole in the bottom. The hose and fittings they use are junk. The bleed screw very badly designed. The shift block was swapped out under warranty, and I replaced all the hoses and fitting myself, which has seemed to slow the leaking way down.

The kindernay chain tensioner basically disintegrated after a few hundred KMs. Had to replace with a reverse components unit. Which seams alot better deigned.

The kindernay hub leaked all its oil out before it even made its first 500km oil change. All that was left was grey paste, full of ground up metal. Sad face.