Why is it a "bottom bracket" and not a "crankshaft"?

[DCBassman]

In all the cycling stuff I've read, the name of this piece has never been adequately explained.
Tell me it's something simple, and I'll shut up...

 

[Yellow Saddle]

A crankshaft has the crank built into the shaft.
On a BB, you only have a shaft.*

Note: A crank is the thing a pedal attaches to and it has no arm. It is an arm.

*Of course it makes no sense, it doesn't explain the bracket part. But hey, BB sounds cool.

 

[MichaelW2]

Crankshafts convert linear to rotational. On bicycles you only deal with rotational forces.

 

[MontyVeda]

this is a crank...

@Yellow Saddle
The 'bracket' bit is the casing the shaft sits in.

 

[DCBassman]

Ok, so we know it's part of a "crank set".
Still doesn't explain "bottom bracket"...

 

[MontyVeda]

Ok, so we know it's part of a "crank set".
Still doesn't explain "bottom bracket"...

bottom of the frame, with a bracket holding a shaft

 

[DCBassman]

bottom of the frame, with a bracket to hold the shaft

Think it might be as simple as someone saying that, and it sticking...bottom, fair enough

 

[DCBassman]

Ok, managed to dig it out. Bracket refers to the brazed lugging used to form the shell / connect the tubes on traditional steel frames, apparently. But is now used for frames made with any technology.
Was just a case of asking Google the right question...
Every day's a school day!

 

[twentysix by twentyfive]

Ok, managed to dig it out. Bracket refers to the brazed lugging used to form the shell / connect the tubes on traditional steel frames, apparently. But is now used for frames made with any technology.
Was just a case of asking Google the right question...
Every day's a school day!

Us old timers don't need Google for that. But we probably do for other stuff

 

[Paulus]

Ok, managed to dig it out. Bracket refers to the brazed lugging used to form the shell / connect the tubes on traditional steel frames, apparently. But is now used for frames made with any technology.
Was just a case of asking Google the right question...
Every day's a school day!

I was just getting around to answering your question, but you found the answer anyway.

 

[cyberknight]

this is a crank...

View attachment 504838


@Yellow Saddle
The 'bracket' bit is the casing the shaft sits in.

i know people who like a nice shiny shaft @Fnaar

 

[DCBassman]

this is a crank...

View attachment 504838

An Ashtabula crank, no less...

 

[CXRAndy]

Another description is chainset bearings

 

[classic33]

this is a crank...

View attachment 504838


@Yellow Saddle
The 'bracket' bit is the casing the shaft sits in.

If this is true,

Crankshafts convert linear to rotational. On bicycles you only deal with rotational forces.

Wouldn't that be a crankshaft. Vertical reciprocating motion of the legs converted to circular motion.

 

[Gasman]

Well, if there's a Bottom Bracket, is there a Top Bracket?