Cannondale Si cranks to PF30 BB conversion questions

Discuss light weight issues concerning mountain bikes & parts.

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fpmesiIII
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Joined: Tue Nov 29, 2011 3:35 am

by fpmesiIII

The bb shell is 73mm wide on the MTb.

What pieces from the cannondale si crank system do I need to properly install.

The cranks will be 170mm long. The frame uses 142mm rear drop outs.

I'd like to get the narrowest possible Q factor (narrow hips) with these cranks.

It is a PF30 bb system.

I will be using a 110BCD cannondale chainring and a 38t narrow wide wolf tooth chain ring set up in single ring format.

What length spindle and how many washers and do I need a curved shim to make this system work?

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yourdaguy
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by yourdaguy

I am not sure,but I think that on MTB you need a wider spindle. Not sure if the SI bearings will work with PF 30 or if you need to get PF30 bearings.
For certain parts stiffer is more important than lighter.

by Weenie


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Anders
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by Anders

Maybe the 109mm road spindle will work, but it really depends on if the arms will clear the chain stays.

jooo
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by jooo

A stock 109mm spindle won't work with a 'normal' MTB. Some people even have clearance issues on road frames using Cannondale cranks (more so with the older, shorter spindles).

AFAIK, both are discontinued, but you can still find 122mm and 128mm spindles which is what you should be looking at. Even these have issues on lots of frames. I think the 122mm spindle was meant for a 68mm shell which means you need to machine the lip off in order for it to work properly on a 73mm shell. Depending on your frame you could run into issues with both arm and chainring clearance, especially if you want to use a 38 tooth chainring!

These pics are from MTBR. It's a Flash29 that uses a machined 122mm spindle, Leonardi XX1 spider (which has less offset than a Cannondale spider) and 32 tooth chainring - not a lot of room.

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fpmesiIII
Posts: 6
Joined: Tue Nov 29, 2011 3:35 am

by fpmesiIII

I bought a 131mm and 132mm spindle. I am most worried about the chainring clearance. the chain stays flare out quickly and a lot with that 142mm rear axle. does anyone know if the narrow wide tooth profile is taller than regular tooth profile. this could be even more of an issue. I'd like to go 36, 38, 40, and 42T chainring. I might be out of luck on the bigger rings. does anyone know to solve this annoying problem of trying to get narrrow q factor and big gear chainring?

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