Shimano GRX chain issue

[Dakrisht]

Or just go 1x with a bigger range cassette. Currently an Ultegra 11/34 paired to a 48/31T in the front.

[Dakrisht]

It's definitely chain line making noise perpetuated bt the Hollowtech cranks. Derailleur is out. Rear hanger is out. BB axial play is out.

[alcatraz]

The grx chainline is only +2.5mm.

Great info. Are you sure though? Shimano specs 46.9mm for the RX810-2.

[WorkonSunday]

Just checking, since no one mentioned these two items: is it possible the hanger is ever so slightly bent? and a silly one to check, upper pulley wheel is still as per original and has been kept clean?

[DaveS]

I got the 2.5mm value from a shimano publication, so yes I'm sure. This link contains a question with the wrong value. Zinn includes a link to the correct shimano info.

https://www.velonews.com/gear/technical ... -calipers/

[disq]

46.9 seems correct for 2x front chainrings. And it's 49.7 is for 1x. I've heard about the "+2.5mm" thing before but it's not exactly that, as all road chainrings (ie. FC-R8000 Ultegra) have 43.5mm chainline specified in the same 2020-2021 catalog. So the difference is actually +3.4mm... See screenshot.

[Dakrisht]

Just checking, since no one mentioned these two items: is it possible the hanger is ever so slightly bent? and a silly one to check, upper pulley wheel is still as per original and has been kept clean?

I don't have a rear derailleur tool to check exact alignment, however, eyeing it looks in-line, it's also a brand new bike so I don't think there are any issues with the hanger.

After cleaning the drivetrain, re-lubing generously with Rock 'n Roll dry, fine-tuning the front mech and even fine tuning the rear - noise from the front/crank is definitely reduced. I actually think the initial Muc Off C3 lube might not have penetrated deep enough in the drivetrain and casued noise (in addition to chainline, etc.)

The bike is still a bit louder than my Ultegra bike or my Campagnolo bike.

This is probably attributed, as other have said, to the chainline on the GRX 2x setup + the HollowTech cranks emitting more noise due to their design + potential debris, sand, dust, etc. when going gravel and moving back to tarmac.

There is absolutely no rub of any kind, even in extremes from the front, it is fine tuned to the T...

But the combination of the above (debris + chainline + design of this group) will make nosie. Nothing will ever be super quiet.

I'm probably expecting a dead quiet front or rear cassette which is not possible.

[Dakrisht]

I wonder if a Dura Ace chain will quiet things down even furhter...

[DaveS]

You can't eyeball a misaligned RD hanger. If you've never checked the hanger alignment, you missed step one.

[DaveS]

46.9 seems correct for 2x front chainrings. And it's 49.7 is for 1x. I've heard about the "+2.5mm" thing before but it's not exactly that, as all road chainrings (ie. FC-R8000 Ultegra) have 43.5mm chainline specified in the same 2020-2021 catalog. So the difference is actually +3.4mm... See screenshot.

Screen Shot 2021-05-13 at 14.14.22 .png

Highly possible, but the +2.5 also comes from shimano literature. I set my grx rings in 2.5mm and it all works great. I even used the cranks without any spacers, but my stock force FD almost didn't have enough travel. It still worked OK.

[pdlpsher1]

You can't eyeball a misaligned RD hanger. If you've never checked the hanger alignment, you missed step one.

+1. I was the first one to reply to this thread and said the hanger alignment needs to be checked and ruled out. I help service my friends' bikes and the first thing I do before I do anything else is checking the alignment. And thus far I haven't seen one bike with a straight hanger.

[Dakrisht]

You can't eyeball a misaligned RD hanger. If you've never checked the hanger alignment, you missed step one.

+1. I was the first one to reply to this thread and said the hanger alignment needs to be checked and ruled out. I help service my friends' bikes and the first thing I do before I do anything else is checking the alignment. And thus far I haven't seen one bike with a straight hanger.

I'm aware you can't eyeball a hanger alignment.

Will get this looked at.

So you haven't seen one new bike with a straight hanger? Doubtful.

[pdlpsher1]

So you haven't seen one new bike with a straight hanger? Doubtful.

Yes. I go by a 1mm tolerance at the rim. The hanger alignment tool multipies any hanger misalignment at the rim. I measured the multiplication factor to be around 6. So a 1mm tolerance at the rim is only 0.17mm at the hanger. Your issue may or may not be due to the hanger. But even if it's not it's always a good thing to check it as a perfectly straight hanger with help with shifting and noise.

[Erwin]

I second that! It is a shame that new (complete) bikes still come with misaligned hangers. I new replacement hanger and an arbitrary frame also needs an alignment correction cause of production tolerances. It is very important for quiet shifting through the complete cassette. A 12spd XTR chain (CN-M9100) would be also an improvement in your situation.

[Dakrisht]

1mm tolerance is a check on the rear hanger.

I'm thinking it's simply just a noiser drivetrain than my Ultegra, perhaps due to the chain line.

It is what it is!