Bicycle Mechanics - Bottom bracket - triple to double

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RVachon
01-12-11, 10:56 AM
Hi everyone;
I have a 2003 Rocky Mountain Metro which I converted from a hybrid to a road bike....well it's an ongoing process. According to Bikepedia (http://bikepedia.com/QuickBike/BikeSpecs.aspx?Year=2003&Brand=Rocky+Mountain&Model=Metro&Type=bike), the bottom bracket is a square taper 73mm x 113mm spindle, with a cheap triple 48x28x28 Shimano Nexave crank. Well, the BB is in need of replacement (sloppy), and the chainrings are getting a little worn.

Found a good deal on a DuraAce 7700 crankset. Can I just get a 73x113 octalink BB to work with this crank or should the spindle be shorter or longer than 113mm since I'm going from triple to double? Anything else I would need?

CACycling
01-12-11, 12:47 PM
No. BB spindle length is determined by the crankset, not the frame. You'd need to find what BB spindle length that crankset requires. Might need to change the FD and shifter to doubles as well.
Al1943
01-12-11, 01:24 PM
The correct spindle length for your 7700 is 109.5 mm. You may be OK with the 113.
http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_1TG0H_001/SI_1TG0H_001_En_v1_m56577569830646804.pdf
The ideal chainline for a double is 43.5 mm, center plane of bike to half way between the two chain rings.

Alan@TreeFort
01-12-11, 01:33 PM
No. BB spindle length is determined by the crankset, not the frame. You'd need to find what BB spindle length that crankset requires. Might need to change the FD and shifter to doubles as well.

This is true, but you can generally fudge it if you are not ready to switch out the shifters and derailleur. Front shifting is not ideal, but it can work. You will set the limit screws higher with a double, restricting the shifter to 2 clicks instead of 3. Depending on the shfiter/deralleur/crank combo, it may not work. But its worth a shot if you aren't ready to switch those parts out yet.
desertdork
01-12-11, 04:31 PM
Hmmm, I thought Shimano's D/A 7700 crank (and all Shimano "octalink" cranks) required a "V1" spline interface which was made for 68mm bb shells (70mm Italian, too). The wider 73mm Octalink bottom brackets were made with a "V2" interface for Shimano mtb cranks only, right? If so, how would the OP make an Octalink BB compatible with his frame and road crank? Remove 5mm of material from the bb shell?