120mm BSA Bottom Brackets

[ParagonMachineWorks]

I recently was faced with the ever so lovely task of determining whether or not a 120mm threaded bottom bracket was something that would be useful for the fat bike market. With initial research pointing towards difficulties finding compatible bottom brackets and cranksets we had decided not to produce any of them. After some awesome feedback from the frame building community and component manufactures we decided to make a small run of them! I won't waste time repeating what has already been stated, so if you want to read a little more about it, head over to the original thread over on MTBR to find out about crank/BB compatibility.

[fortyfour]

Thanks for this Sam - What is interesting is the last fat bike I made for myself sports a 190mm rear axle spacing and I spec'd the 190mm specific Race Face Cinch cranks/spindle combination. Now truth be told, the first ride out I had this immediate feedback: I had absolutely NO power in my pedal stroke. The bike felt completely dead when I attempted to stand up and get on the gas. Yes, the 190mm specific spindle allows for a monster amount of tire clearance. However, that tread on that crank was so wide that I felt it negatively impacted the feel of the bike when pedaling. With a little research, I found that the 170mm specific spindle actually would fit my bike, have good chain line and allow for a lot less tread. The bike now is sporting that "shorter" 170mm specific spindle and feels A LOT better beneath me - personally I don't even notice it. For 5" tires and 190mm rear ends, there needs to be something between a 100 and 120mm bottom bracket shell width and a slightly longer spindle than Race Face's Cinch 170mm specific crank. The 190mm specific spindle is just too long (IMO). That's my own opinion based on building and riding (snow specific). For most applications, be it 170mm with 4" tires or 190mm with 5" tires, you can make a 100mm bottom bracket work and get plenty of tire clearance. In Ti, that's a different animal due to the larger stay diameter. But for the record, the Race Face Cinch Turbine 170mm specific spindles will work for 5" tires and 190mm rear axle spacing. Chainline really is dependent on how short you're making your stays. (Me, I actually lengthened them for this prototype quite a bit from the last version).

But my own opinion, I think there needs to be something in between 100 and 120mm's and a slightly different length spindle for a Race Face Cinch crank than what they are now supplying for their 190mm specific cranks.

[VertigoCycles]

Kris, that's true, but really only with the 1x ring flipped to the outside. A non 1x front setup and a 190/197 back end requires the 190 spindle for the correct chain line.

[fortyfour]

Kris, that's true, but really only with the 1x ring flipped to the outside. A non 1x front setup and a 190/197 back end requires the 190 spindle for the correct chain line.

Apologies: I was speaking/typing ONLY in reference to a 1x setup. I forget sometimes people want a double... But I have to say, I have been absolutely LOVING my XX1 setup with a 30 and 28t chainring. I did not have to flip the ring to get a good chain line. I should probably post some pics at some point of the ring, chain line and crank clearances on this bike for the sake of the conversation.

I still say that the 190mm spindle feels completely odd beneath me though and I had no power what so ever. I was getting stalled on stuff that never, ever gives me problems. As soon as I swapped spindles, things felt "normal" again. (For the record, this is Race Face's Turbine Cinch crank we're speaking of which has a lot of tread to begin with.) And I'm not convinced 120mm is the right width based on what I have built. Press fit: yes. Outboard bearing/english thread: No.

[VertigoCycles]

Apologies: I was speaking/typing ONLY in reference to a 1x setup. I forget sometimes people want a double... But I have to say, I have been absolutely LOVING my XX1 setup with a 30 and 28t chainring. I did not have to flip the ring to get a good chain line. I should probably post some pics at some point of the ring, chain line and crank clearances on this bike for the sake of the conversation.

I still say that the 190mm spindle feels completely odd beneath me though and I had no power what so ever. I was getting stalled on stuff that never, ever gives me problems. As soon as I swapped spindles, things felt "normal" again. (For the record, this is Race Face's Turbine Cinch crank we're speaking of which has a lot of tread to begin with.) And I'm not convinced 120mm is the right width based on what I have built. Press fit: yes. Outboard bearing/english thread: No.

This is going from (my shady) memory but the 190 BB spindle works something like this on a 100mm shell...Three 2.5mm spacers are required under the cups, then there are two 11.5mm spacers required between the cups and the crank arms. So that's 30.5mm of spacers total for the 190mm spindle. A 120mm BSA shell reduces that to 10.5 and gives the spindle more support.

I've made some 120mm PF30 shells for fat bikes and in hindsight, I'd change them to 130 for the 170 spindles and 150mm for the 190 spindles. Unrelated to the usefulness on the bike is the issue of overlap on the BB post of my Journeyman and the fact that my Shuz Tung alignment table takes 100mm width shells max. I've made a new spacer for my fixture but the BB post on my table is hardened and turns the chips into exciting fireballs when the carbide lathe tools touch it.

[VertigoCycles]

and hey...isn't it nice to just build a damn road bike once in a while?

[steve garro]

and hey...isn't it nice to just build a damn road bike once in a while?

I wouldn't know, do tell.

- Garro.