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Old 07-27-22, 02:41 AM
Bike Gremlin
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Join Date: Nov 2010
Location: Novi Sad
Posts: 4,267

Bikes: Custom made on Scott Speedster frame, Custom made on a 1996. steel MTB frame (all but frame changed at least once in the past 20 years).

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Originally Posted by beanbag View Post
Does anybody know what is the typical left-right offset on Shimano road cranks? (in particular the GRX gravel cranks)
For example, the right crankarm might be a little further from the chainstay than the left one. (Assuming chainstays are symmetrical)
In my case, I have an older MTB where the triple crankset has a Q factor of 182 and seems to be offset to the drive side by 4-5mm. The left (non drive) crank is 15mm from the chainstay and the right is 24mm. (I check against the rim and the offset is similar)
I want to upgrade this to a Shimano GRX double with Q factor 151mm. IF the GRX crankset also has a 5mm offset, then this won't work as both sides would move in by 15mm and the left arm will now hit the chainstay while the right will have 8-9mm clearance. BUT if there is no offset, then both sides will have about 4-5mm clearance.

P.S. I read that there should be a spec in some Shimano technical documents about the distance from the inside edge of the crank arm to the centerline, which I guess is a more relevant number and doesn't have me guessing at the crankarm thickness, etc.
If it's of any help:

I'm running Sora compact cranks, Shimano Hollowtech II type, on a bike with 68mm wide BSA threaded BB shell.
I mounted Tiagra RS500 hollowtech BB cups, without the 2.5 mm spacers on either side.

This reduced the overall Q-factor by 5 mm, and it still works perfectly fine.

However, the pin used to "just in case" catch the left crank should it start sliding off needed to be removed - because the axle protruded further than Shimano designed it for (though still not too much for the plastic end cap to allow for adjusting the bearing preload).
If the pinch bolt and the plastic end-cap don't save me, and I fail to notice it's getting loose, I should have a crank arm fall off!
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