bmx bottom bracket sizes

[stevepeanut]

Has anyone got any information on the sizes of bmx bottom brackets? either old skool or new.

A friend of mine is starting his own business making frames, and he has done a hand full of mountain bike and racer frames. He buys a ready made moutain or road B/B and then tubing and makes the frame from there. I am trying to pursuade him to have a go at making me a one off bmx frame. He is asking me what sizes bmx B/Bs are. I dont know the answer to that.

I guess racers are totally different, but I am wondering if any mountain bike and bmx B/Bs are the same.

Any help would be greatly appreciated, as I am really lost off on this.

[TwoBobRob]

Theoretically, you could have whatever you want....

The most common crank axle size is 19.05mm diameter (3/4") so any cartridge bearing with that I.D. would work.

for the record, a conventional 19mm mid BB requires a R12 - 2RS bearing, so the BB shell would be machined to carry that bearing.



 

[not johndub71]

Keep it american! Big bearings and better load spread.

[TwoBobRob]

John - a modern mid BB uses the same american size bearings of old, just without the ally cups. We're talking sealed of course, not loose ball 

[not johndub71]

Thats my happiness spoilt then :-(

What about roller bearing or a needle set up? Could something current be reengineered?

[TwoBobRob]

Yeah, I've always thought a nice little taper roller bearing setup would be good, but in reality it'd all to be too big and clunky for bmx I think.