Bottom bracket sizing question

[aferrick]

I think this is a simple question for you guys, but I've been having a bit of trouble getting my head around this. For figuring out if a BBS02 will fit a bottom bracket, which dimension should match/be in range?

From pictures from Amazon sellers it looks like the Diameter of the bottom bracket should be 34-36mm and the length (width?) is 68-73mm. The length of the BBS02 spindle is 68mm, which makes sense for this matchup.

But when I'm looking at the specs of bikes and their bottom brackets they have different numbers so I'm not sure if they'll fit. For example, 2019 Trek Marlin 6 has a bottom bracket "VP BC-73, 73x1XXmm, Square Taper" and if you click its link the dropdown lists either 68mm or 73mm x 113mm to 127.5mm. Is this 68mm "bottom bracket cartridge length" x 113mm "tip to tip" length? Do they not list the cartridge diameter because it's a given that it'll fit in a standard size bottom bracket?

From Googling it looks like people have fit BBS02s just fine to these bikes, but I just wanted to make sure before purchasing anything.

 

[Dewey]

Yes, I fit a 68-73 BBS01 motor first to a bike with a 68mm wide bottom bracket and I didn’t need any extra hardware. Then I swapped the motor to another bike with a 73mm wide bottom bracket and I needed to buy some 5mm longer M6 screws than the ones you got with the kit which are probably for 68mm, and some M6 washers so you can attach the fixing plate to the wider bottom bracket. Also with a 73mm you will likely have to omit the second M33 locking nut as you won’t have enough screw thread, it’s fine provided you tighten the main M33 locking nut, although you might also want to fit a BSB-1 torque arm https://california-ebike.com/shop/bsb-1-bafang-stabilizer-bar-bbs0102-bbshd/

 

[aferrick]

Yes, I fit a 68-73 BBS01 motor first to a bike with a 68mm wide bottom bracket and I didn’t need any extra hardware. Then I swapped the motor to another bike with a 73mm wide bottom bracket and I needed to buy some 5mm longer M6 screws than the ones you got with the kit which are probably for 68mm, and some M6 washers so you can attach the fixing plate to the wider bottom bracket. Also with a 73mm you will likely have to omit the second M33 locking nut as you won’t have enough screw thread, it’s fine provided you tighten the main M33 locking nut, although you might also want to fit a BSB-1 torque arm https://california-ebike.com/shop/bsb-1-bafang-stabilizer-bar-bbs0102-bbshd/

Thanks. So the second number in the cartridge spec isn't important? Only the first i.e. 68 or 73 x abc where the abc doesn't matter?

So the cartridge of a fat tire bike, for instance, might be 90mm x abc and then the 90 means I'd need a different BBS02 or BBSHD spindle?

 

[Dewey]

See https://www.empoweredcycles.com/blo...bracket-standards-and-bafang-mid-drive-motors
Also California Ebike sell an adapted motor for 100 or 120mm fat bikes https://california-ebike.com/shop/bafang-8fun-bbs-02-fatbike-mid-drive/

 

[tomjasz]

 

[tomjasz]

BBS02 or BBSHD

BBS02 68mm - 73mm
There are 100mm and 120mm conversation kits for BBS01 and BBS02. But I’d not build out a fat bike with a BBS02 or BBS01

BBSHD 68mm - 73mm, 100mm, and 120mm

 

[aferrick]

BBS02 68mm - 73mm
There are 100mm and 120mm conversation kits for BBS01 and BBS02. But I’d not build out a fat bike with a BBS02 or BBS01

BBSHD 68mm - 73mm, 100mm, and 120mm

The listed numbers being the length of the bracket marked in red on the 3rd picture?

I guess what I'm wondering is what do the dimensions of the cartridge that fits into a bottom bracket refer to? In my original post the cartridge dimensions are listed at 68mmx113mm, I'm assuming the 68mm in that dimension matches up with the BBS02 spec, but what is that 113mm?

Edit: I think I was able to find it https://bikeraceinfo.com/images-all/tech-images/bottom-bracket/campy-bb.jpg it does indeed refer to the overall axle length.

 

[tomjasz]

but what is that 113mm?

Nothing you need to fret over. What’s important is the type of bottom bracket. Square taper or press fit. Se Deweys link.

 

[tomjasz]

The listed numbers being the length of the bracket marked in red on the 3rd picture?

Yes, that’s where you measure to determine which motors are an option. Axle length has no bearing.
68mm BBS02 or BBSHD 68mm and you’re good to go.
Do yourself a favour, watch YouTube install videos. Next search Google BRAND MODEL BBSHD and again, BRAND MODEL BBS02

Finding build threads posted on forums will help you immensely.

 

[aferrick]

Yes, that’s where you measure to determine which motors are an option. Axle length has no bearing.

I get it now. Thanks for the help.