What size tapered bb

brother

Hi, I have a Shimano Ultegra bottom bracket on an old steel bike. I am thinking about changing the crank for something retro. I would have to change my bottom bracket for a tapered one. The bottom of my frame is 68mm but how do I find out what length of tapered bb to buy?

whyamihere

It depends on what cranks you want to fit.

cpeachey

If you look at some of the chainset ads it tells you what BB is needed. If it's too short the inner ring hits the frame. Too long and maybe the front changer does not reach. The shop selling the cranks should be able to advise.
Chris

maddog 2

what is the crank?

Is it double or triple?

Is it road or mtb?

brother

It's a road audax bike with a double compact crankset.

Monty Dog

Without knowing the exact model of crank, it's almost impossible to specify - back in the 80s, the likes of Super Record and the many clones took a 115mm bracket, whereas most more modern, low profile cranks take something nearer 107mm. It also depends on whether your crank takes a ISO or JIS taper - you can swap, but need to compensate in length.

brother

The crankset I am considering is the Sugino Alpina from here:

http://www.velo-orange.com/sualcr.html

desweller

It tells you in the product description:

"The result is this lovely VO-spec 110bcd Alpina. 48/34t rings; square taper JIS 110mm BB; 155mm Q-factor; about 665gm."

maddog 2

JIS = Shimano by the way

you used to be able to get UN-73 (XT-level) in 110mm but they don't stock them new any more, which is a shame. There's the cheaper UN-54 but it a heavy lump. You could also consider RaceFace, FSA Ultimax, Royce, Hope but they are all more cash, usually.