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bmx bottom bracket sizes

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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?

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