Why is it called a bottom bracket?

Bottom Bracket

The bottom bracket is the bit of the frame that your cranks go through – unless it’s the unit inside that contains the bearings, or simply the axle the cranks spin on. It’s not clear. The phrase is used interchangeably for all these things – despite exactly none of them being a bracket.

So why a bracket?
Hilariously, nobody seems to really know, though it’s a peculiarly English thing – other countries use entirely different words to describe it. It’s also a pretty old phrase, and may even predate cranks and go back to push-along ‘velocipedes’; early pedal-less bikes like kids’ balance bikes, but for daring chaps in top hats and tails. A bracket is defined as a usually L-shaped (but at least two-armed) device that joins one thing to another, and clearly the horizontal tube added to frames to hold cranks doesn’t fit that description. A simple, crank-free join between tubes (or bits of wood) would require a bracket, however.

Isn’t it the bearings?
Some people argue this tube laterally ‘brackets’ the ball races/cartridge bearings inside it, and hence the name – but that invokes another, non-mechanical sense of the word (the one that includes these brackets here). And that would be odd. Certainly, many distinguish that section of frame as the bottom bracket shell, implying that the bottom bracket itself lies inside. If you buy a bottom bracket, you will get exactly that – the assembly of bearings on which the cranks spin. But this assembly may or may not include the axle itself, which further muddies the waters as to exactly what constitutes a ‘bracket’. Still, it is at the bottom of the bike, so that’s something. Unless you’re on a recumbent, in which case it’s not, and it’s the bit you punch through little old ladies’ knees when they wander out, having mistaken your bobbing warning flag as a jaunty summer memory of the childhood golf course they weren’t allowed to play on as little girls.

So can we fix it?
It seems very unlikely, despite ‘bottom bracket’ really not meaning anything and being about as confusing and un-self-explanatory as it could get for anyone trying to get their bike fixed. The trouble is nobody else has a particularly good name for it either – the French call it the ‘pedalling assembly,’ while the Italians go 100% vague with ‘movement’. That said, ‘crank bearings’ might work quite well…

  • Joe

    Bottom Unit or Crank Unit/Fitting?