cranks for square tapered BB

For discussions about bikes and equipment.
mig
Posts: 2236
Joined: 19 Oct 2011, 9:39pm

cranks for square tapered BB

Postby mig » 3 Jul 2013, 1:12pm

a little hard to describe but is there a standard orientation in which the holes in cranks are cut for square tapered BBs?

a friend bought a left hand crank in the hope of matching it to an existing chainset.

the hole in the left crank was cut with the 'square' rotated 45 degrees to the chainset's own 'hole' hence giving the effect that the cranks on either side weren't parallel when fitted.

did he cop for a dodgy crank? or do manufacturers merely line up the holes in their own sets? does this by any chance differ for tandems?

(apologies if you are now confused!) :oops:

hamster
Posts: 3521
Joined: 2 Feb 2007, 12:42pm

Re: cranks for square tapered BB

Postby hamster » 3 Jul 2013, 1:17pm

Typically the corner of the BB square points in line with the crank arm - Campag, Shimano, Sugino, Middleburn are all like this, at least for things made in the past 15 years. There are a few (as you have discovered) which don't.

mig
Posts: 2236
Joined: 19 Oct 2011, 9:39pm

Re: cranks for square tapered BB

Postby mig » 3 Jul 2013, 2:24pm

why oh why oh why!!! :)

next you'll be telling me that manufacturers make cassette sprockets slightly different widths apart and stuff like that...... :!:

Brucey
Posts: 39890
Joined: 4 Jan 2012, 6:25pm

Re: cranks for square tapered BB

Postby Brucey » 3 Jul 2013, 10:12pm

the two configurations are often known as 'diamond' (the most common) and 'square-on' types. Quite a lot of the inexpensive suntour cranksets fitted to MTBs are square-on types, and there are a few others.

Yet another trap for the unwary...you just need to check to be sure....

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

mig
Posts: 2236
Joined: 19 Oct 2011, 9:39pm

Re: cranks for square tapered BB

Postby mig » 4 Jul 2013, 9:07am

annoyingly it was a rear tandem left hand crank in 172.5....i can't remember the brand....but it wasn't a cheapo!

WOOLIFERKINS
Posts: 134
Joined: 11 Apr 2008, 10:39pm
Location: Oxon

Re: cranks for square tapered BB

Postby WOOLIFERKINS » 5 Jul 2013, 2:45pm

Don't forget there are two different "standards" of taper as well
Neil