Bafang BBS02 with different BCD

[Vancetp]

Hi all, new here.

I have 2 BBS02 mid drive motors. I bought one last year and the other recently. I was using an offset chainring for the first one, which fit correctly. However, I wanted to move the chainring to the new motor, only to find it doesn't fit! The BCD of the new motor is larger. I've attached 2 photos. The first one has a second chainring b/c it's a tandem synchronized ring, but I hope you can see the chainring hub. It's clearly different from the second one. I can post clearer photos if necessary.

I need a similar offset ring for the new motor b/c of chainline problems, but where can I get one?

Thanks for any help!

Cheers, Phil

 

[Vancetp]

Has no one else seen this?

 

[m@Robertson]

Bafang BBSxx motores don't have a bolt circle diameter at all. They have that 5-bolt pattern at the center and thats it. The BBS02 has one pattern and the BBSHD has another, probably a deliberate effort from the factory to hinder the aftermarket.

But... all BBS02's have the same 5-bolt pattern.

What you are showing us is one motor has one kind of aftermarket chainring, directly bolted to the motor, and the other has a different one. The one you are using presently under the standard spidered crankarm looks to be an offset ring that is meant to move the chainline inboard and reduce chain misalignment. It is alloy and probably a higher level of quality than the other one, which is also an offset ring, but clearly does it differently, being straight-ish stamped steel with a deep lip around the outer edge providing the offset.

That use of a second crankarm with a standard BCD adapter is, as far as I have ever seen, unique (and I have seen a lot of these motors). So you are going to have to play around and just figure this out. In an ideal world, you will figure out the source of that chainring that lets you do this dual ring thing, buy another one and fit it behind the crankarm exactly as you have done it on the other motor.

Failing that you are going to have to wing it and just buy different rings and see what fits.

 

[m@Robertson]

Worth mentioning: The much more typical way to do this is to use a 104, 110 or 130 BCD adapter and just put a single ring on. Then you use crankarms that are meant for this motor. What you have done is move the chainline waaaaay outboard, which is typically very bad and skews the chainline (increasing wear and the danger of breakage throughout the drivetrain). You have also increased the Quack Factor by quite a bit which may be good or bad depending on your personal body traits.

Google BBS02 Chainring Adapter to immediately see the thing I am talking about.

 

[Vancetp]

Hi and thanks for your reply. You have misunderstood what is going on, as well as my question, probably due to my lazy attempt at showing the problem.

I have taken the syncro chainring/pedal assembly off for clarity, and took some more detailed photos to help show what is going on . I wasn't able to put the photos in some kind of order, so here's some description:

The third photo shows the required installation method on a tandem bike. The second chainring is for the synchro chain which connects the front and rear pedals. This chainline is corrected by an adapter that extends the front BB axle.

The first photo shows the new BBS02 and the stock chainring. Note how far the motor axle hub protrudes through the chainring hole. I assume this is a beefed up bearing assembly on newer models.

The second photo shows the old BBS02 (with the syncro pedal.chainring assembly removed this time). Note that the motor axle hub does not protrude.

The fourth photo shows an approximate measurement of 32mm between adjacent bolts for the chainring bolt pattern.

The fifth photo shows an approximate measurement of 37mm between adjacent bolts.

Both motors are BBS02s. The chainrings are not interchangeable. I really need an offset chainring for the new motor.

 

[m@Robertson]

OK I get it now. The pics explain things clearly, and this time I have spotted the real difference here.

Lets look at your first picture. Ignore the chainring and focus on the plastic motor cover clearly visible behind it. That cover is held down by Phillips head screws around the outside edge. This is plainly a standard-issue BBS02, and the ring you are showing is pretty clearly an '02 style ring.

Now lets look at the second picture, and again look at the motor cover, not the chainring. We can see it is held together entirely differently via bigger socket cap hex key bolts. Also that chainring sure does look familiar in its construction, but I'll save that for a bit further on.

This is what your motor cover looks like without any chainring on, right? This pic has a Lekkie spacer on, but thats the same cover as your own secondary housing.

Lets add to this the fact that I said above that the BBS02 and the BBSHD have different bolt patterns to mount up their respective chainrings and...

You do not have two BBS02's. You have a BBSHD and a BBS02. Your first pic is a BBS02. Your second one - the older motor - is a BBSHD. And the chainring on that BBSHD is clearly a Lekkie clone, of which we know there to be many.

All of the differences you cite are due to the fact that you have two different motors.

To answer your original question: You buy a BBSHD offset chainring. AliExpress sells cheap clones. Lekkie sells the originals which you can find at California Ebike or Empowered Cycles, although the price difference from the clones is staggering.

 

[m@Robertson]

Also, now that we know the problem, and a better grasp of your overall situation, I'll note the BBS02 has MUCH less offset in its available offset chainrings due to its different construction. Where a 42T ring like what I think you are showing us typically has about an 18mm offset, a comparable BBS02 ring has only 9mm (the stock ring you have on now only has 5.4mm to put that in perspective). I am comparing Lekkie rings here so other manufacturers will vary.

The bottom line to the above is you are not going to get comparable results. Whether they are workable or not is to be determined. Good luck.

The BBS02 is also much less powerful, and not overbuilt. The BBSHD was essentially a beefed up follow-on to the 02 after the 02 had been on the market for awhile and it was found to have weaknesses that the HD addressed (in particular, blown controllers from being worked hard). A BBSHD is exactly what I'd use on a tandem vs. a BBS02 which is less robust.

 

[Vancetp]

I guess you must be right. I don't know how I ended up with a BBHSD, though. I had one on another tandem, but it had a 100mm BB. I ordered an 02 because the HSD was too powerful for my needs. I guess they sent me the wrong one.... I'll have to look more carefully at it! It's very hard to see underneath as it's hidden by the frame.
Thanks for all your trouble for such a simple problem (not a problem).

 

[m@Robertson]

I ordered an 02 because the HSD was too powerful for my needs.

I would count having the HD a bonus. Its not about the power, its about the robust internals. You can kill a BBS02 with a hard duty cycle, and that is well nigh impossible with a BBSHD.

Take a look at this. If you haven't done so already, you can completely change the behavior of the BBSHD so it is a smooth-engaging and downright tame performer on pedal assist. You will end up with a motor that will last forever as its running at a fraction of its capacity. Those same settings will work for a BBS02 although the chief benefits are the smooth engagement given it is not as robust.

https://talesontwowheels.com/2023/08/09/bbshd-settings-for-a-pedaling-cyclist-2023-edition/
The version linked above is not a soup-to-nuts explainer. There is another earlier edition on that site from a couple years earlier that does that job. The 2023 settings are the result of a lot of refinement over time.

Thanks for all your trouble for such a simple problem (not a problem).

With any luck it will do you some good

 

[Vancetp]

Many thanks!