Bafang BB xx dual chainring mod

G

gabryeludrea

100 µW
Joined
Jun 15, 2014
Messages
7
Hello ebike diy ers!

I am in the process of making a project for converting my touring bicycle into an ebike and as I am a fan of mid drives I found Bafang BBS very appealing.
Only problem that i find with it (wich is a big turnoff) is that it uses only one chainring, and 46 or 48 is quite large for my needs anyway. As I said I will use it with a touring bike and I m not looking for speed, instead I want the capability to aproach some very challenging hills (up to 30%) if needed, and for this the stock chainring is maybe too large. So this is what I was thinking:
1) Changing the stock chainring with a 36 or 38T for general terrain and adding another 28T, for climbing steep hills. Gear shifting should be possible with the front derailleur.
2) Adapting my triple chainring Shimano Deore that I have on the bike right now, to be mounted on the BBS, also making gear shifting with front derailleur possible.

Another good reason for needing theese mods is that I still want to preserve my bike s climbing abilities in case my battery dies or the motor is damaged.

Did anyone tried one of the two described above?
Do you have any ideea if any of them is possible?
Or, if not, can you please recoment me a mid drive model that corresponds to my needs?

Thank you, I will appreciate a lot!
 
Warren said:
This has been discussed pages back on here. Even if you can get it to work, the chainline will be horrible. Go with a SRAM Dualdrive.

http://www.sram.com/sram/urban/family/dd3
Click to expand...
Very interesting concept, thanks for your recomandation!
But this system allows similar gear ratio to a classic configuration (2 or 3 chainrings in front combined with minimum other 7 in the back)? I am more interested in the climbing abilities than in the speed aspect.
 
RLT said:
Or would this work for what you intend?

http://endless-sphere.com/forums/viewtopic.php?f=31&t=60703
Click to expand...
Thanks, but I'm not sure how this can be adapted to work with the Bafgang BBS. Also, the price seems alot higher than I expect to spend for solving my problem.
 
Get a 42t chainwheel from here: http://www.alcedoitalia.it/shop/guarniture/corona-42-denti-per-bafang-centrale-bbs01/

Get a mountain bike rear derailleur and an 11-36 cassette, and you will be on your way. For even more climbing ability, change the largest cog on the cassette with an up to 42t cog. Search for "cassette 42t" on Ebay.
 
tahustvedt said:
Get a 42t chainwheel from here: http://www.alcedoitalia.it/shop/guarniture/corona-42-denti-per-bafang-centrale-bbs01/

Get a mountain bike rear derailleur and an 11-36 cassette, and you will be on your way. For even more climbing ability, change the largest cog on the cassette with an up to 42t cog. Search for "cassette 42t" on Ebay.
Click to expand...

Good point with the 42T chainring. Thank you!
About the 42T cog on the cassete, I imagine that the shifting will not be possible anymore due to it s large size, so, it has to be done manually, wich is not so nice.

I like very much the idea suggested by Warren, regarding the dual drive system, it s a brilliant solution. It s like having your front derailleur hidden in the rear hub. Very convenient because you can have aproximately the same gear ratios and climbing abilities, keeping it simple and comfortable in the same time. You have your shifter in one place, using only one hand for shifting gears while the other is free for operating motor controlls - throttle or PAS levels. And together with that 42T chainring in the front, it should climb threes also.

Still, I am worried about one thing, how would the chainline be with only one chainring in front and a cassete of, let s say minimum 7 in the back? First and last speeds will put some strain on that chain, because it will not run straight, but more like in diagonal. With a triple chainring front derailleur is simple to keep a nice chainline because you can group the large one in front with the small ones in the back, and so on for the middle and small chainring, but on this sytem, with only one chainring in front I think the chain will suffer. Does anyone have some experience using it, do you know if it creates problems on the chain by using the extreme up and down chainrings in the cassete?
 
A Rohloff hub is the ultimate solution for chainline with this drive, but very pricy. Nothing else, but an IGH, will improve the chainline. As with most such drives, the motor and/or reduction gear forces the chainring to be out further than normal. A bike with a longer chain run, like a cargobike, or recumbent can solve that problem. You could go with a 7 speed cassette with a spacer behind, to prevent the chain from moving toward the centerline as far. But the Dual drive is no longer offered with a 7 speed shifter. And the 8 speed uses the same chain as a 5/6/7 speed. You could dump the 11 tooth first cog (it creates too much chain wear anyway) and put a spacer behind the remaining cogs to make a 7 speed out of an 8 speed, and set the rear derailleur's inner stop screw to prevent an overshift. Frankly, I think you will be fine running any 8/9/10 speed cassette in back (they are all the same overall width). You may need the front derailleur, or some other chain keeper, to prevent the chain coming off in low. But that is a good idea, with a single chainring in any event.
 
gabryeludrea said:
Good point with the 42T chainring. Thank you!
About the 42T cog on the cassete, I imagine that the shifting will not be possible anymore due to it s large size, so, it has to be done manually, wich is not so nice.
Click to expand...

The cog is placed next to the 36t cog, and one of the middle cogs (17t for example) is removed to make room for it. I have made cogs like that myself and they shift just fine.



gabryeludrea said:
Still, I am worried about one thing, how would the chainline be with only one chainring in front and a cassete of, let s say minimum 7 in the back? First and last speeds will put some strain on that chain, because it will not run straight, but more like in diagonal. With a triple chainring front derailleur is simple to keep a nice chainline because you can group the large one in front with the small ones in the back, and so on for the middle and small chainring, but on this sytem, with only one chainring in front I think the chain will suffer. Does anyone have some experience using it, do you know if it creates problems on the chain by using the extreme up and down chainrings in the cassete?
Click to expand...

Single front chainring is very common on mountain bikes these days, and I don't think you need to worry about it causing problems as long as the chainline is correct. The chainline with Bafang drives is a problem though. I measured the chain line on my bike, which has a normal 68mm bottom bracket, and it is roughly 51.5 mm, not 50 mm as I thought it would be. The ideal for a road bike rear hub is 43.5-45 mm and for a mountain bike rear hub about 47.5-50 mm. The chain is severely diagonal when I use the larger rear cogs, so I will make a new chainwheel myself to improve the chain line. I have a road rear hub.
 
The problem was solved before Bafang or GNG or Cyclone ever got in the game. Stokemonkey demonstrates how it's done. Use a tandem left crank or BMX RH/LH compatible crank to allow the motor to drive the left side. Then use whatever crank and chainring/derailleur setup you like on the right.

499059913_864a7fbb7b_m.jpg
 
tahustvedt said:
Get a 42t chainwheel from here: http://www.alcedoitalia.it/shop/guarniture/corona-42-denti-per-bafang-centrale-bbs01/

Get a mountain bike rear derailleur and an 11-36 cassette, and you will be on your way.
Click to expand...

I've got that exact set up and I've found nothing that it can't climb (and it still does 25mph+) - you'll run out of traction way before gearing.

IMAG07211_zpsa82edb0d.jpg


I don't see any requirement for a dual ring set up, unless you're intending to ride unassisted.
 
I too would go with the large cog on the cassette, the Dual Drive III creates drag while pedalling unassisted, so I removed mine on my Bosch bike with the penalty of 20 mph limit, which suits my cadence and dodgy knees. I would be limited by the steepest of terrain, but It copes with most of my riding with a 11-32 cassette, but I will seriously consider the cassettes as mentioned here !

One other thing with the Dual drive, Bosch won't install these on their new performance motors and limit to the older motors with 50nm torque. The Bafang 750 is supposed to have, what, 70 nm ?
 
amigafan2003 said:
tahustvedt said:
Get a 42t chainwheel from here: http://www.alcedoitalia.it/shop/guarniture/corona-42-denti-per-bafang-centrale-bbs01/

Get a mountain bike rear derailleur and an 11-36 cassette, and you will be on your way.
Click to expand...

I've got that exact set up and I've found nothing that it can't climb (and it still does 25mph+) - you'll run out of traction way before gearing.

IMAG07211_zpsa82edb0d.jpg


I don't see any requirement for a dual ring set up, unless you're intending to ride unassisted.
Click to expand...
What would be your suggestion for a bike that's primarily used unassisted? I will be owning both a mtb and a road/tour bike.
 
Warren said:
A Rohloff hub is the ultimate solution for chainline with this drive, but very pricy. Nothing else, but an IGH, will improve the chainline. As with most such drives, the motor and/or reduction gear forces the chainring to be out further than normal. A bike with a longer chain run, like a cargobike, or recumbent can solve that problem. You could go with a 7 speed cassette with a spacer behind, to prevent the chain from moving toward the centerline as far. But the Dual drive is no longer offered with a 7 speed shifter. And the 8 speed uses the same chain as a 5/6/7 speed. You could dump the 11 tooth first cog (it creates too much chain wear anyway) and put a spacer behind the remaining cogs to make a 7 speed out of an 8 speed, and set the rear derailleur's inner stop screw to prevent an overshift. Frankly, I think you will be fine running any 8/9/10 speed cassette in back (they are all the same overall width). You may need the front derailleur, or some other chain keeper, to prevent the chain coming off in low. But that is a good idea, with a single chainring in any event.
Click to expand...

Hi there. I been checking the forums and am interested in getting a bafang 750 because of its programmable capabilities, though have been reluctant because of the geared system and mostly because of the chain rings.

From what i read (and i hope i read it right) is that my Yuba Mundo cargo bike can still keep the 3 chain rings with the Bafang motor installed? Just adjust the front derailleur out a bit more?
 
Chalo said:
The problem was solved before Bafang or GNG or Cyclone ever got in the game. Stokemonkey demonstrates how it's done. Use a tandem left crank or BMX RH/LH compatible crank to allow the motor to drive the left side. Then use whatever crank and chainring/derailleur setup you like on the right.

499059913_864a7fbb7b_m.jpg
Click to expand...


Hey there.. you have my interest in this setup, though unsure how it could be freewheel with the motor thrusting the cranks forward meaning if you used a throttle it would force you to pedal right?
 
38 front is the lowest gearing with a tight chainline. That should be enough to get up any hill. If you want to improof something get rid of the smallest gear of your cassette and move it more to the outside, that does improf the chainline.

Im made an 6 Speed cassette out of an 8 speed and added an 42T in the back. So thats 7 speed moved one out with 13-42T now.

With 42front and 34rear I can climb Hills where i fall over.
 
Miles said:
c0mpute said:
Hey there.. you have my interest in this setup, though unsure how it could be freewheel with the motor thrusting the cranks forward meaning if you used a throttle it would force you to pedal right?
Click to expand...
Yes.
Click to expand...
Thanks. I like the idea of the bracket holding the hub.. though dont like to be forced to pedal at 20kph or so. Though it does give an idea of how i could put a 1000 watt hub into the center of the yuba on the right side ..just got to get the bracket and the size of the hub to the size of the yuba
 
42t on the rear is doable with the right derailleur, that is made for very "steep" cassettes. Search for a derailleur that is rated for 36T chanrings. I dont have the product code in mind but there is one that is around ~$30 from shimano, made for 9-speed
 
46T chainring and 34T cassette gear can pull my 17 stone up a 25% hill no problem.
With these crazy low gear setups you will have the front wheel in the air all the time.
 
I had a customer send me some info recently of a dual chainring on his BBS powered recumbent.

He used one of my 104BCD chainring adapters and a dual chainring in conjunction with a fatbike (100mm) derailleur setup to shift it all outboard a bit. Seemed pretty happy and sent me a rundown as he felt it was a useful option for the adapters.

He now runs both 48T and 32T on his BBS setup. Torque and speed options.

 
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