Old 04-03-20, 01:10 AM
Master Parts Rearranger
RiddleOfSteel's Avatar
Join Date: Mar 2015
Location: Seattle, WA
Posts: 3,734

Bikes: 1985 Trek 620 - 25.5"

Mentioned: 199 Post(s)
Tagged: 0 Thread(s)
Quoted: 1227 Post(s)
Liked 811 Times in 469 Posts
Shimano offers external-bearing bottom bracket designs meant to thread into a traditional BSA or Italian-spec threaded bottom bracket. Campagnolo offers a similar external-bearing bottom bracket design as well. Shimano, at the very least, keeps things user- and installer-friendly with their Hollowtech II design (first generation of 10-speed, 7800 Dura-Ace), with any Hollowtech II BB working with any Hollowtech II crankset. 24mm spindle width for all.

Press fit bottom brackets tend to be more bearing cartridges and they, like their name, press into the frame. No threading. Press fit BBs come in many styles and widths. It's byzantine, but that's modern bikes for you.

Outside of Shimano, 30mm crankset spindle diameters seems to be the norm. You can find aftermarket external-bearing threaded bottom brackets that will accept a 30mm spindle diameter. They're nice, and naturally uncommon, and thus expensive. But fitting a killer looking SRAM Red or FSA SLK crankset (among others) on a frame would be sweet. I've looked into it/am looking into it. As to how long the spindle is, how wide that BB is overall, and what's needed--if anything--to make it all play nice, that'll be up to you. Perhaps a different subforum.

I'd look at the crankset(s) you want, find the specs for the spindle, see if there are any bottom brackets that take it, and see if it's possible. Maybe the mechanics forum, maybe the modern road bike forum. PF BB knowledge and experimentation is going to be pretty limited here as it is C&V after all (I've used a BB30 conversion kit on a '15 Cannondale CAAD10 to make it run a 24mm spindle instead of a Creakasaurus Rex BB30). Outside of a vintage Klein, we'll point you in a hopefully helpful direction and wish you the best.
RiddleOfSteel is offline