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Discussion Starter · #1 ·
This is a xpost from the Turner forum, but I wanted to solicit input from S Work crank owners. Maybe I'm missing something.

The bb (factory Specialized BB30) and crank with spacers are correctly installed. I even took it to a reputable Speci mechanic for a second opinion. Nope, not a thing wrong. Are any S Work crank users having issues with flex under extreme torque?

Here is my explanation at the Turner forum:

I have a Czar, size large, and the 2013 S-Works 175mm crank being used is rubbing the right chainstay under extreme hard pedaling. At first I thought it was the rubber boot crankarm protector, but even after cutting away the boot's inside I'm still having the inside of the crank arm touch the right/DS chainstay.

The crank and bb are properly installed. The S Works crank is a 166 or 167 factor, and there is proper distance between the chainstay and crank arm in all situations except the aforementioned in-saddle and out of saddle situations with extreme torque. I'm 162 pounds and a XC racer so it's not like I'm an insanely powerful torque monster.

I'm aware the S Works crank on a Czar combo is pretty rare. At this point I'd rather not use a Shimano crank with my Praxis conversion due to this particular Czar being spec'd as a lightweight marathon racer.

A reply pointed toward the oem BB being a flexy SRAM item. Maybe that's the cause? Kind of hoping so since it'd be an easy fix.

Thanks in advance.
 

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How much clearance do you have between the arm and chain stay? On my 14 SJ HT there's about 2 cm. Could also be your frame flexing that's causing the rubbing and not the cranks.
 

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Discussion Starter · #3 ·
Don't have bike here to measure, but on the DS it's at least 3mm. A nice gap. As for the frame flexing...the Czar is lauded as a laterally stiff frame. But I have posted in the Turner forum in regard to other Czar owners with their respective cranks and stiffness.

All pivot bolts are properly torqued. It's odd; the S Works crank is known for not being a laterally flexy item, and I know there are so many variables in lateral flex when it comes to the bike as a whole. The non-drive side has a titch more space between the chainstay and doesn't even come close to touching under extreme torque.
How much clearance do you have between the arm and chain stay? On my 14 SJ HT there's about 2 cm. Could also be your frame flexing that's causing the rubbing and not the cranks.
 

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You should be able to reposition the spacers on the spindle to push the RHS out a little relative to the LHS, and that should fix it.

As you're probably aware the crank will always tend to "torque in" to the RHS, (not the LHS) due to the position of chain on the RHS. This torque "moment" (to use a term from physics) will be accentuated when using low gears, as the torque you are applying is greater. In these situations this torque "moment" will cause your rear triangle to flex outwards (to the RHS) dragged by the chain. So, in other words, your crank "strike" is caused, not by a flexi crank, or frame, but by the rear triangle.

So, technically, you frame isn't flexing, it is your rear triangle (including the bearings & pivots) flexing.

On an "ultra-torque"-style crank (as the SW crank is), you have relative freedom to place the spacers where you need them to ensure appropriate chain stay clearance. Your LBS should have pointed this out to you.

FWIW, I have an SW crank on a SW Epic and have around 4-5mm clearance on the RHS and no strike, although, out of the box, I had to re-adjust the BB & spacers to stop strike.

HTH
 
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