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RADBMX.CO.UK  |  Technical & Reference Section  |  Tech and Restoration  |  bmx bottom bracket sizes
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Author Topic: bmx bottom bracket sizes  (Read 1405 times)

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Offline stevepeanut

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bmx bottom bracket sizes
« on: September 29, 2012, 07:35 PM »
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.

Offline TwoBobRob

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Re: bmx bottom bracket sizes
« Reply #1 on: September 29, 2012, 08:09 PM »
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.



 


Offline not johndub71

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Re: bmx bottom bracket sizes
« Reply #2 on: September 29, 2012, 08:45 PM »
Keep it american! Big bearings and better load spread.
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Offline TwoBobRob

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Re: bmx bottom bracket sizes
« Reply #3 on: September 29, 2012, 09:15 PM »
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  ;)


Offline not johndub71

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Re: bmx bottom bracket sizes
« Reply #4 on: September 29, 2012, 10:29 PM »
Thats my happiness spoilt then :-(

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

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Re: bmx bottom bracket sizes
« Reply #5 on: September 30, 2012, 01:46 PM »
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.


RADBMX.CO.UK  |  Technical & Reference Section  |  Tech and Restoration  |  bmx bottom bracket sizes
 

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