RADBMX.CO.UK
Technical & Reference Section => Tech and Restoration => Topic started by: stevepeanut on September 29, 2012, 07:35 PM
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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.
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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.
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Keep it american! Big bearings and better load spread.
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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 ;)
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Thats my happiness spoilt then :-(
What about roller bearing or a needle set up? Could something current be reengineered?
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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.