3

I'm trying to install an absoluteblack oval chainring on a GRX FC-RX810-1 crankset.

After assembling and tightening the bolts I noticed there's a gap between the chainring and the crankarm. Basically, only 1 out of 4 bolts puts the chainring totally flush, the other 3 have about 1mm gap (see the photos below).

I'm wondering is this acceptable or should be considered a defect?

Thank you.

enter image description here

enter image description here

enter image description here

enter image description here

6
  • 1
    Did you loosen the bolts and rattle the ring around a little, to get it to "settle in"? Mar 12, 2021 at 12:47
  • I tried several times, but to no avail. I even tried to put it the other way around, just in case. The thing is, I can position it properly before putting the bolts in, and it looks good. But as soon as the bolt protrudes into the crankarm the gap appears. My guess is that the original GRX chainring and the crankarm had the threads drilled in one go, so they are in sync. Apparently the new chainring bores have threads with a slightly different phase and thus there's no smooth transition between the chainring thread and the crankarm thread, but it's just a guess. Mar 12, 2021 at 12:52
  • 8
    Something doesn't sound right if you're attaching two threaded parts together like that. It's not done in engineering for good reason (except in some single-bolt fixings) and I've never seen it in the limited number of chainrings I've worked with, nor can I think why it would be made that way
    – Chris H
    Mar 12, 2021 at 13:26
  • 1
    This could be a matter of opposing extreme manufacturing tolerances making the parts incompatible.
    – Carel
    Mar 13, 2021 at 8:42
  • 3
    Chris H is right. If the chainring and crank arms are both threaded, then thats either a really unusual assembly or two incompatible components. You could drill out the chainring threads and bolt it on flush like most chainrings ensuring concentricity if youre running a single sprocket at the back. The last thing you want on a single up front is an undulating chainring with no derailler to stop it throwing the chain off.
    – RoRo
    Mar 14, 2021 at 5:22

2 Answers 2

2

For future reference, these particular chainrings will fit just about any Shimano 4 bolt EXCEPT the GRX. They mount a bit strange compared to many chainrings as you can see in this image, the bolt comes through the crankset from behind and screws into the chainring.

enter image description here

Compatibility

Shimano Dura-Ace 9100, R9120, R9150 & R9170 Di2, Ultegra 8000, R8020, R8050 & 8070 Di2., >105 R7000, R7020, R7070, Dura-Ace 9000, Ultegra 6800, Shimano 105 5800, Tiagra 4700 ; 10 >/ 11 / 12spd compatible. In short ALL Shimano 4 bolt cranks except GRX.

Chainring has 1.5mm offset towards frame for perfect chainline.

Source: Absolute Black

4
  • You appear to be correct. I'd assumed that the OP got an Abs Black chainring that was designed for GRX, since I thought the bolt circle diameter was not 110mm like on the road cranks. It seems like only the BCD for the inner ring is actually different, however.
    – Weiwen Ng
    Mar 29, 2021 at 20:53
  • Do the GRX cranks have a different BCD or something? I wonder what makes them incompatible.
    – MaplePanda
    Mar 30, 2021 at 0:23
  • @MaplePanda a) spider geometry is a bit different. B) inner BCD is 80mm or so.
    – Weiwen Ng
    Mar 30, 2021 at 13:30
  • Thanks for pointing out, Nate W. Seems like the description on the product page on bike-components.de is not entirely correct as they have the exact same list, but with "all other Shimano 4-arm cranks with 110 mm BCD" at the end. I asked them to fix it. Mar 30, 2021 at 15:08
1

Thanks everyone for your help, this indeed doesn't look normal. I ordered a wolftooth oval chainring instead. It has no threads in the bores and fits perfectly.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.