Bicycle Mechanics - Cranks/BB size XD Crank 120mm spacing
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11-19-07, 08:19 AM
I have a Motobecane Grand Touring from the 70's with 120mm rear spacing for the days of 5 speed freewheels. I am thinking of putting a Sugino XD2 110/70 triple crank to help my aging knees. What size BB? Yes, there is the Swiss threading to deal with. I see on the Yellow Jersey site of having 108/113 size straight axles. Also,I own a Phil Wood 108 BB with the Swiss retaining rings. What size to use on the 10 speed era bike? The chainrings will be something like 48-6/36/26-4. I will probably use a 5 speed freewheel 13-28 or 13-32 range. Will my Phil work with this set up. Any suggestion for front derailleur? Thank you for your input.
11-19-07, 12:20 PM
I'd stick with the Phil BB. If the 108 doesn't work with that crank check with Phil to see if they can replace the spindle for you. Their parts are built to last and they do service what they sell.
I'm not certain what the normal chainline for 120mm spacing is but you can probably find the answer to that on Sheldon Brown's site. If your bike originally came with 2 rings up front, you could have problems with clearance next to the chainstay unless you move the crank outboard a bit so watch for that.
Any FD built for 'compact' cranks should work as long as it mounts to your tubing size. I'd get one that has a flexible mount instead of a cast mount in case your tubing diameter is a bit off of current standard.
11-19-07, 07:36 PM
Here's Sheldon Brown's write-up on chainline: http://sheldonbrown.com/gloss_ch.html#chainline
The unknown variable is the offset of the cranks once they've been mounted on your BB. Trial and error is your best bet. I'm using a Sugino XD on a 110mm spindle with an 8 speed cassette on the rear, and the crank is still too far outboard for me, since I use the outer two rings more often. I could probably move in 1 or 2 millimeters, but I can't afford Phil.
As for FD's, I'm using a Suntour Cyclone MKII on the stock 46/36/26 setup, and it works admirably well. However, I've had to mount it higher than normal to avoid interference with the RD cable, a problem you'll find if you have above the chainstay cable routing (because the FD will be mounted lower). Someone suggested I try this Suntour XC Expert Microdrive FD (http://cgi.ebay.com/Suntour-XC-Expert-Front-Derailleur-Clamp-on-28-6-New_W0QQitemZ150169016988QQihZ005QQcategoryZ27950QQrdZ1QQssPageNameZWD1VQQcmdZViewItem) available on ebay. I bought one, but haven't yet mounted it. (Oh, and mine came with the clamp bolt, despite the item description).
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