Join Date: Oct 2009
Location: England, currently dividing my time between university in Guildford and home just outside Reading
Bikes: Too many to list here!
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
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.
Last edited by Airburst; 08-23-13 at 12:09 PM.