Bottom braket sizes???
08-21-13, 01:04 PM
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Bottom braket sizes???
What are the sizes of the BB shells on BMX and folding bikes? I want to use a Metropolis crank that needs 68mm? not to fit a MTB.
08-21-13, 01:26 PM
#2
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BB size is both shell width (side to side) and inside diameter (and threading). BMX and folding bikes probably have more variation than road/mtb bikes as to BB specs. How do you not know what the dimensions of the bike are? Can you give us a make/model or clear pic? We need info about the situation and what you want to accomplish to provide you with a full answer.
Last edited by cny-bikeman; 08-21-13 at 01:54 PM.
08-23-13, 11:37 AM
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this is the crank... I do not have a bike for it yet.
https://www.metropoliscomponents.com/patterson.htm
https://www.joe-bike.com/2012/03/11/r...peed-crankset/
https://www.metropoliscomponents.com/patterson.htm
https://www.joe-bike.com/2012/03/11/r...peed-crankset/
Last edited by jawnn; 08-24-13 at 11:27 AM.
08-23-13, 12:05 PM
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BMX bottom brackets are a complete smorgasbord of standards.
Most modern BMX bikes don't have one-piece cranks anymore if they're proper BMX bikes rather than BMX-shaped objects. Some of them do still use a one-piece-crank BB shell with cartridge bearings pressed in and a 3-piece crankset, known as a "USA" or "American" BB in BMX terms, some of them use "Mid" or "Spanish" BBs, which are smaller-diameter press-fit standards, and some of them use a conventional threaded BB, referred to as a "Euro" BB by BMX manufacturers.
Folding bikes tend to have conventional threaded BBs if they're at all decent (you may still find one with a one-piece crank shell though), the 68mm quoted by the OP is, I assume, the width of the BB shell required by the planetary gear system they want to use, and the good news is that most threaded BB shells are 68mm wide unless they're on an MTB.
Most modern BMX bikes don't have one-piece cranks anymore if they're proper BMX bikes rather than BMX-shaped objects. Some of them do still use a one-piece-crank BB shell with cartridge bearings pressed in and a 3-piece crankset, known as a "USA" or "American" BB in BMX terms, some of them use "Mid" or "Spanish" BBs, which are smaller-diameter press-fit standards, and some of them use a conventional threaded BB, referred to as a "Euro" BB by BMX manufacturers.
Folding bikes tend to have conventional threaded BBs if they're at all decent (you may still find one with a one-piece crank shell though), the 68mm quoted by the OP is, I assume, the width of the BB shell required by the planetary gear system they want to use, and the good news is that most threaded BB shells are 68mm wide unless they're on an MTB.
Last edited by Airburst; 08-23-13 at 12:09 PM.
08-23-13, 12:10 PM
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08-23-13, 12:15 PM
#7
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I want to use a Metropolis crank that needs 68mm? not to fit a MTB.
they include an external type BB. I believe.. modified to transmit the planetary counter torque.
Perhaps you are confused just because the only picture is of an MTB install. https://pattersonbike.com/
you realize 73 is more than 68 and spacers fill space?
Have you discussed this with the seller ?
and perhaps its best to have, them, a Professional Shop install it for you.
Last edited by fietsbob; 08-23-13 at 12:22 PM.
08-23-13, 01:21 PM
#8
Mechanic/Tourist
You don't need a general answer - it's not important what BMX or folding bikes have but what the bikes you might consider have. Pull up the specs or check with the manufacturer/seller to find our BB width. I would guess a BMX bike would be best with the 165mm cranks, but make sure you are getting the benefit you expect from that kind of money.
08-24-13, 11:41 AM
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Perhaps you forgot to read the article about the crank. After the 4th photo it states:"Compatibility: fits any standard 68 mm bottom bracket shell."
I send an inquiry to the makers of the crank.
Looks like BMX bikes are not going to work.
I send an inquiry to the makers of the crank.
Looks like BMX bikes are not going to work.
Last edited by jawnn; 08-26-13 at 11:45 AM.
