Crank Arm Clearance Conundrum

[thermalattorney]

My steel disc road frame doesn't have a lot of crank arm/chainstay clearance due to short 410mm chainstays. Been running Shimano's non-series RS500 cranks for 3 years, as they were the only Shimano branded cranks that could clear the chainstays.

Just switched from Di2 to eTap and wanted to be matchy-matchy so I picked up a pair of S952 "wide axle" cranks with a 30mm spindle, a FSA BSA30 BB, and pile 'o spacers. The frame-building specs list the S952 arms as having 62.5mm worth of clearance on the DS, which is more than the 60.2mm Shimano quotes for the RS500.

Once installed the S952 cranks don't appear to have more clearance and worse, the DS arm makes a tiny bit of contact with the chainstay under heavy load. The S952 cranks are installed with the correct spacer/wavy washer combo. Even reconfiguring the spacers to move the DS arm a tiny bit outboard doesn't fix it. :mad:

Here are some pics of the cranks both unloaded and loaded: https://photos.app.goo.gl/gCG8Ec5u1NZKUHLq5

Why is there so much more flex in the S952 cranks and am I SOL?

Is it worth contacting a local frame builder about getting the DS chainstay dimpled a bit more, or are there other crank options that offer compact gearing but more chainstay clearance?

Thanks! :help:

[AngryScientist]

it's probably the frame flexing, not the crank...

i would just get a set of WI VBC cranks and the proper length BB and call it good. a little heavier, but no big deal, and you will have dealt with the problem for life.

[kppolich]

Had something similar here, except the 952's fixed my problem. FYI SRAM carbon mountain bb30 cranks also worked.
https://forums.thepaceline.net/showthread.php?t=227115

[kramnnim]

How do we feel about removing material from the crank arms? On some models of cranks, it looks like the arms are all the same length, and they just drill the pedal holes in different places to get 165-180mm...

[marciero]

How do we feel about removing material from the crank arms? On some models of cranks, it looks like the arms are all the same length, and they just drill the pedal holes in different places to get 165-180mm...

Grinding some material-angled/beveled on inside- is totally viable option on alloy cranks. I wouldn't try it on carbon though. As far as the one-arm-length-with-different-hole-placings, I am pretty sure that no quality cranks are made that way.

[John H.]

I am not 100% familiar with the SRAM 952 crank. Is the spindle fixed on one of the crank arms?

How about moving to a crank where you could vary the spindle length? Something like the Easton Cinch or Cannondale SISL crank?
That way you could run a long enough spindle to solve your clearance issues.

In my opinion, your frame builder dropped the ball- He did not consider width of the stays vs. what crank you might be running.

[thermalattorney]

Thanks everyone for the replies. It makes sense that these cranks are stiffer and it's the frame doing the flexing.

After some more googling it's clear that I don't actually have the "Wide Axle" cranks as the eBay seller advertised. Those have the phrase etched on the BB spindle. Instead I have the normal axle width S952. :crap:

I'll contact them to see if the can be returned, if not they'll go up on the classifieds until I can afford to get the correct model.

[kppolich]

950 are normal length.
952 are the wide axle.

900 are the normal length previous gen.
902 are the wide axle length previous gen.

^At least for GXP I know.

What bottom bracket do you have on your bike Threaded, Press fit?