Rupert

I've been reading Sheldon Brown and searched bikeforums but I'm still a little confused. Looking to do my first bike build and recently purchased last year's (2009) Caad9 frame on discount, but i'm not quite sure what size bottom bracket / crank type is compatible. I was told it's an English bottom bracket so I guess I need a 68mm x ?? bottom bracket.

If it helps: I'll be using a 9 speed 12-26 cassette, the bike is 60cm, and I want a double crank set in the front with 175mm crank arms, preferably shimano. Any guidance would be greatly appreciated, thanks!

msummers

yes, english 68mm. crank size is relative to your inseam, different fitters will recommend different lengths. just google 'crank arm length calculator' to find some online charts for an idea of what your size might be.

Steev

The way to do it is to select a crankset and then get the BB in the length and interface specified for that crankset. Pretty well any crankset will work on your frame.

operator

That has nothing to do with what he's asking about, did you even read his post?

Any non-bb30, modern road crankset.

joejack951

If you buy one of the new(er) Shimano Hollowtech II cranksets, you don't need to worry about bottom bracket length. BB length mattered back in these days of square taper, ISIS, and Octalink cranks but the Hollowtech II crank spindles are integrated into the drive side crank arm. The bearings are seperate cups that thread into the frame then the spindle is inserted through the cups. The non-drive side arm is then clamped onto the spindle. Chainline is non-adjustable but assuming your frame's BB shell is faced properly, the resultant chainline will be correct.

Don't forget that Shimano does not include the BB cups with their cranks. They must be purchased separately. As far as I know and have experienced (though my knowledge does not currently include the new Ultegra 6700 or Dura Ace 7900), any of the Shimano BB cups can be used with any of their Hollowtech II cranksets. Someone please correct me if I'm wrong.

Rupert

Thanks for the help everyone. Another question: I've been noticing that a lot of the double crank sets say "10 speed compatible" but i have a 9 seed cassette. It seems like the 105/ultegra are 10 speeds and the tiagra/dura ace are 9 speeds, is this correct?

operator

No.

capwater

9 speed cranks work with 10 and vice versa. Reality is there is no such thing as 9 or 10 speed cranks, it'a all shimano marketing to insinuate that 10 speed cranks are those with an external BB.

Steev

Dura Ace gets the newest bling first, then it trickles down to the others.

Rupert

Wow, that's good information to know, thanks for the responses everyone. So cranks marketed as "9" and "10" speed, (assuming they’re both double chain rings and the same generation/model), could use the same front derailleur and bottom bracket? What about with compact crank sets, do they need different front derailleurs?

joejack951

The bottom bracket has nothing to do with how many cogs are in your cassette. The ideal chainline is the same regardless of 8/9/10 speeds. Almost all "10 speed" cranks use integrated axles anyway.

The front derailler is dependent on which size chain you use, which is typically determined by how many cogs are in your cassette. You'd use a 10 speed FD with a 10 speed cassette and chain.

Compact cranks do not need special deraillers. A few manufacturers used to offer "compact" versions of their FD but now even they admit that the same derailler will work for both.