Monday, September 8, 2014

Rebuilt Crank for Red

I rebuilt the entire crank for Red from existing crank parts and some new ones. I'm trying see if I can get by without having to go with a Schlumph Mountain Drive to achieve a comfortable climbing gear. With the rebuilt crank I now have a respectable 18.5 gear inches on the low end and 120.9 on the high end. The Schlumph has some drawbacks for me which I'll get into in a later post.

The new crank is now a 48/39/24. The amount of chain needed to handle this crankset with a 36/11 cassette is right on the edge of what a long cage derailleur can handle. You can go up to a 50t on the crankset but if you don't want a loose, sloppy and noisy idle chain then you need to avoid going small/small (24t chainring/11t cog) with your gears. (note: chain length must first be adjusted to accommodate a largest chainring/largest cog gear combination).

I left the front derailleur mounted higher on the derailleur mast then it might normally be mounted for a 48t large chainring. Mounting the derailleur a bit on the high side allows it to clear the outer guard. However my main concern was the angle of the shifting cable coming from the cable stop that Catrike mounts on the mast to accommodate a 52t large chainring. Moving the derailleur down on the mast increases the angle at which the cable exits the cable stop increasing wear. 

I've put a few miles on this crankset and the derailleur height on the mast seems to be non-issue. The shifting is smooth even when shifting down or up between the 39t and the 24t chainrings. 

When building up your own crank it's a good idea to have chainring spacers on hand. I get spacers here from Wheels Manufacturing Inc.

Details:
Bottom Bracket - Mega Exo BB-8681 (68mm  English)
Crank and spider - FSA SL-X Carbon
Outer guard - Custom Catrike Guard
48t Chainring - FSA Road Pro, 130mmBCD outer, 10 speed
39t Chainring - FSA Road Pro, 130mmBCD middle, 10 speed
24t Chainring - Salsa, 74mmBCD, 9 speed (works fine with 10 speed)
Inner gaurd - Volae 74mmBCD



I like this old style Catrike outer guard. The newer one is a bit plain.


Gear inches with the re-built crankset.


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