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Decreasing the Chainline on a Shimano GRX Crank

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Decreasing the Chainline on a Shimano GRX Crank

Old 04-26-23, 05:54 PM
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Decreasing the Chainline on a Shimano GRX Crank

I'm running a Shimano FC-RX600-11 crank + GRX front derailleur with a shimano 105 R7000 setup, on a Cannondale Synapse. I really like the lower gearing that the 46/30 crank provides, but I wish it didn't have the "wide" 47mm chainline. I know, it's not a huge deal, but I'd like the chain to run quieter and with less wear that a chainline that has the big ring closer to the center of the cassette.

I noticed that both chainrings are on their own set of bolts, and both install from the inside. So I'm wondering, could I get some spacers, maybe around 3mm, plus some longer chainring bolts, and move both rings inward?

Has anyone tried this? Does anyone see a problem with this plan? I understand that I may need to switch to a "road" front derailleur that has the right swing (I have a spare one I can use). Yes, I know I could just buy a different brand's 46/30 crankset, but I've read that many of those also have the wider chainline, plus chainring bolts + spacers would be less money than a new crank. Plus I like how Shimano chainrings shift.



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Old 04-26-23, 07:33 PM
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how much clearance is there between the rings and the chainstay?

are there any spacers between the Drive side BB bearing housing and the BB?

press fit or threaded BB?
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Old 04-26-23, 07:43 PM
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Originally Posted by maddog34
how much clearance is there between the rings and the chainstay?

are there any spacers between the Drive side BB bearing housing and the BB?

press fit or threaded BB?
According to my measurements, I could move the chainrings in at least 5mm and still have 1-2mm of clearance around the frame.

No spacers anywhere on the BB. It's an English threaded 68mm BB shell.
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Old 04-26-23, 09:42 PM
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Originally Posted by xg5a
According to my measurements, I could move the chainrings in at least 5mm and still have 1-2mm of clearance around the frame.

No spacers anywhere on the BB. It's an English threaded 68mm BB shell.
good thing that it has room to move.. the bad thing is that with no BB spacers, it won't be simple and inexpensive to move...

some really old 2-3 sp. cranks used some cool 3mm spacers and extra-long ring screws... some used nice fitting 1 to 1.5mm washers... and most MTB Bash Guard kits use extra-long ring screws...Hit up a local co-op and bring food or beer, or both

just remember whatever spacers you use must fit fairly well to the screws or you'll probably end up with a series of nasty squeaks and creaks...

Last edited by maddog34; 04-26-23 at 09:51 PM.
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Old 04-26-23, 09:52 PM
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I've been running that crankset with an otherwise Ultegra drivetrain for years without any unusual wear or excess noise. Did you adjust the H-limit screw on the front derailleur?
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Old 04-26-23, 11:57 PM
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have a RX810 crank on a Topstone with mix of other 10 and 11 speed components
and the drivetrain is relatively quiet (when using both small and large chainrings)

R7000 crank would be an option (and a significant upgrade compared to RX600 crank) - but small chainring would 34t or 36t (compared to 30t of the RX600 crank) ...

what cassette are you using ? could use an 11-30 or 11-32 cassette ... 34-32 low is fairly low (approx 28 gear inches) ... ???

Last edited by t2p; 04-27-23 at 12:01 AM.
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Old 04-27-23, 01:40 AM
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PS.. that big ring is THRASHED... the chain, also. you got your money's worth outta them,.
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Old 04-27-23, 06:04 AM
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Originally Posted by maddog34
just remember whatever spacers you use must fit fairly well to the screws or you'll probably end up with a series of nasty squeaks and creaks...
This is exactly the sort of concerns I was hoping would be raised here about the chainring spacers route. When you say the spacers must fit tightly to the screws, do you mean in terms of the inside diameter of the spacer matching the outside diameter of the bolts?

I had similar thoughts - with spacers, the crankset spider itself would no longer be supporting the chainrings. So it would just be a matter of friction with the chainring touching the spacers, and the spacers touching the spider. Of course, having the bolts really tight would help as it would maximize this friction. But still, I think if this plan goes wrong, this is where the issue will be.

Here's an example of bolts and spacers that I was thinking of using (I wouldn't need the nuts). https://www.ebay.com/itm/184989039679

Originally Posted by maddog34
PS.. that big ring is THRASHED... the chain, also. you got your money's worth outta them,.
Interesting that you say this. It's a brand new chain. And the chainring has about 1000-1500 miles on it. I didn't think that was anywhere near long enough to cause significant chainring wear? The old chain didn't have any measurable stretch when I took it off, I just needed a different length chain as I moved these parts from a different frame to this one.
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Old 04-27-23, 06:12 AM
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Originally Posted by Polaris OBark
I've been running that crankset with an otherwise Ultegra drivetrain for years without any unusual wear or excess noise. Did you adjust the H-limit screw on the front derailleur?
The noise I mention isn't due to anything rubbing - the FD works totally fine. The issue is just that there is significant cross-chaining when riding in the big ring and anywhere past the middle of the cassette.



Originally Posted by t2p
have a RX810 crank on a Topstone with mix of other 10 and 11 speed components
and the drivetrain is relatively quiet (when using both small and large chainrings)

R7000 crank would be an option (and a significant upgrade compared to RX600 crank) - but small chainring would 34t or 36t (compared to 30t of the RX600 crank) ...

what cassette are you using ? could use an 11-30 or 11-32 cassette ... 34-32 low is fairly low (approx 28 gear inches) ... ???
Thanks for the suggestions, but I think a 34t small ring would be a no-go in this circumstance. This is my wife's bike and she really likes the current gearing for going up the steep hills around here while pedaling at 90rpm. I already have an 11-34 cassette on the bike.

I'm curious about why you say the R7000 crank is such an upgrade over the RX600 crank though? I would have assumed they are fairly similar in construction?

That being said, in terms of swapping out the crank, I do also have an new FSA gossamer pro (current model) in 50/34t. I wish I could find some 46/30 chainrings for a decent price, as I think that this would give me a normal "road" chainline (although I'm not sure if they shift as well as Shimano rings?). But I can only find them for $56 each, which is getting close to the cost of the crankset for two rings.

And yes, the drivetrain is "relatively" quiet - I do admit that I'm being a bit of a perfectionist with this chainline change. Things are just a little too cross-chained in the big-big gear combos, so I'm looking to optimize things if possible.

Last edited by xg5a; 04-27-23 at 06:19 AM.
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Old 04-27-23, 06:29 AM
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Does your bike have the current 142 spacing? On my Topstone the big ring is aligned with the third smallest cog. I guess this is about right if using the double crank as intended, as opposed to trying to use the full 11 cogs with one ring. I guess if you use the small ring strictly as a bail out moving the chainline might be OK but I'd be concerned about losing the useful downshift-then-trim feature. Maybe add a chain catcher?

Last edited by shelbyfv; 04-27-23 at 07:32 AM.
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Old 04-27-23, 06:40 AM
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Originally Posted by Polaris OBark
I've been running that crankset with an otherwise Ultegra drivetrain for years without any unusual wear or excess noise. Did you adjust the H-limit screw on the front derailleur?
I’ve been running the GRX 11 speed crankset (with the GRX FD) for several years… Same experience as you: works like a charm. Quiet and smooth. I wonder if the OP is simply imagining that this is a problem?
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Old 04-27-23, 06:59 AM
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Originally Posted by xg5a

Thanks for the suggestions, but I think a 34t small ring would be a no-go in this circumstance. This is my wife's bike and she really likes the current gearing for going up the steep hills around here while pedaling at 90rpm. I already have an 11-34 cassette on the bike.

I'm curious about why you say the R7000 crank is such an upgrade over the RX600 crank though? I would have assumed they are fairly similar in construction?
st of the crankset for two rings.
yes - the 11-34 is a great bailout / climbing gear - one of the advantages of the R7000 RD (as opposed to 6800 RD which Shimano maxes at 32t)

the R7000 crank - as well as the RX810 crank - are ‘hollow tech’ (?) cranks and weigh approx 1/4 lb less than the RX600 crank ... the R7000 and RX810 large chainrings are also higher quality (not sure about the small rings)

Last edited by t2p; 04-27-23 at 07:30 AM.
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Old 04-27-23, 07:04 AM
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maybe too much riding in the big ring ? ... too much cross chaining ?
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Old 04-27-23, 07:07 AM
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Originally Posted by xg5a
And yes, the drivetrain is "relatively" quiet - I do admit that I'm being a bit of a perfectionist with this chainline change. Things are just a little too cross-chained in the big-big gear combos, so I'm looking to optimize things if possible.
offer an incentive to avoid big-big lol
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Old 04-27-23, 07:28 AM
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Originally Posted by xg5a
That being said, in terms of swapping out the crank, I do also have an new FSA gossamer pro (current model) in 50/34t. I wish I could find some 46/30 chainrings for a decent price, as I think that this would give me a normal "road" chainline (although I'm not sure if they shift as well as Shimano rings?). But I can only find them for $56 each, which is getting close to the cost of the crankset for two rings.

And yes, the drivetrain is "relatively" quiet - I do admit that I'm being a bit of a perfectionist with this chainline change. Things are just a little too cross-chained in the big-big gear combos, so I'm looking to optimize things if possible.
First, will that FSA even take a 30T chainring? If the bolt circle is 110mm, the smallest chainring that will fit is 33T and 34T is far more common.

Second, that's a lot of trouble to go to to reduce cross chaining in a gear that shouldn't be used.
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Old 04-27-23, 07:50 AM
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FWIW, the RX810 is 710g, the RX600 is 806g.
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Old 04-27-23, 09:52 AM
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Originally Posted by Koyote
I’ve been running the GRX 11 speed crankset (with the GRX FD) for several years… Same experience as you: works like a charm. Quiet and smooth. I wonder if the OP is simply imagining that this is a problem?
105 is inherently a little bit noisier.

I very much doubt he wore out the chainring, especially the large one.
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Old 04-27-23, 09:59 AM
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Originally Posted by Polaris OBark
105 is inherently a little bit noisier.

I very much doubt he wore out the chainring, especially the large one.
Your post reminds me -- I forgot to mention that the rest of my drivetrain is Ultegra, as is yours. Works like a champ.

I had my bike built a week or two after GRX was announced, and the shop thought the 48-31 crankset would work better than the aftermarket crank (Praxis) that we'd been planning to use. So they built the bike with a placeholder Shimano 50-34 crankset (a pull-off from a new bike they'd sold), then installed the GRX crankset and FD when they became available after a few months. I noticed no difference in shifting performance, nor anything else. Which is why methinks the OP is a bit OCD about this.
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Old 04-27-23, 10:33 AM
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Originally Posted by xg5a
This is exactly the sort of concerns I was hoping would be raised here about the chainring spacers route. When you say the spacers must fit tightly to the screws, do you mean in terms of the inside diameter of the spacer matching the outside diameter of the bolts?

I had similar thoughts - with spacers, the crankset spider itself would no longer be supporting the chainrings. So it would just be a matter of friction with the chainring touching the spacers, and the spacers touching the spider. Of course, having the bolts really tight would help as it would maximize this friction. But still, I think if this plan goes wrong, this is where the issue will be.

Here's an example of bolts and spacers that I was thinking of using (I wouldn't need the nuts). https://www.ebay.com/itm/184989039679






Interesting that you say this. It's a brand new chain. And the chainring has about 1000-1500 miles on it. I didn't think that was anywhere near long enough to cause significant chainring wear? The old chain didn't have any measurable stretch when I took it off, I just needed a different length chain as I moved these parts from a different frame to this one.
ID-wise.. as to that chainring... notice that the valley between each tooth is no longer symetrical? the rear wall is more vertical and the front wall of the valley is more laid over toward the front? that's wear.
Also note HOW the chain rollers seat in those valleys? the chain sets high in those valleys towards the exit off the bottom of the ring... A new large chainring might help eliminate most of that gap, since you say the chain is new... Mileage is less of a factor on any bike used off-pavement than visible wear... and all us online mechanics have to go by is the pics posted... Chain ring tooth wear is extrapolative.. the more wear there is, the faster it will wear due to less teeth being presented to the chain under load... the effective diameter of the chainring is reduced because of the wear... at some point the chain's sideplates begin hitting the chainring when the ring has a machined ridge like yours does.... all the wear increases "CHAIN NOISE", which is why you're wanting to alter the chainline, right? "Chain noise" is the chain slipping up and down in those tooth valleys under load, or rubbing against the der. cages, btw,,, I've seen some Tragically worn out chains in the past that made noise, but that chain is "new"....

Based on the pics and info provided, I advise trying a new large Chainring before you move Both chainrings.
Just Curious.. What brand/model/ # of speeds, chain is that? Peened pins, flat sideplates, no markings visible..

and i completely agree with the other responders that mentioned using the small ring more often.. it shows next to no use..

Last edited by maddog34; 04-27-23 at 11:09 AM.
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Old 04-27-23, 11:09 AM
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Not a solution here but I "triple-ized" an old SR/Sugino 110/74 crankset to be a super low Q fix gear. Three rings so I could have three very different gears for mountain up, down and flat with three very different cogs on horizontal dropouts. I did not use the inside 74 BCD holes. Instead I spaced the third ring outside the usual outer ring. (No FD and perfectly straight chainline so being very close the crank is just fine. And crankset sits inboard that much more. Knees love it.) To do this I went to Ace Hardware and bought (IIRC) 8mm flat head screws and good looking SS cap nuts. These bolts were only to provide the "squeeze". The key element to getting bolted chainring assemblies to behave, not creak and not slowly self-destruct is to have a tight, near press fit cylinder inside the crank and ring holes so nothing can slide around. To do that, I had sleeves machined to the exact 10mm (again, IIRC) of the bolt holes and a looser fit over the 8mm bolt. (The material is absurdly exotic - titanium! But only because TiCycles' Dave Levy did the work and had the perfect ti tubing on hand to start with plus all the ti machining equipment since ti bikes is what he does.)
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Old 04-27-23, 11:10 AM
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That is how the chainrings look when they are new, by design.
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Old 04-27-23, 11:57 AM
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Originally Posted by maddog34
the rear wall is more vertical and the front wall of the valley is more laid over toward the front? that's wear.
But that more vertical part of the tooth is the bit that does the work, and it's not showing signs of wear (except that the ring looks to have been bashed around a bit).
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Old 04-27-23, 05:37 PM
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In lieu of an attempt to decrease the chain line at the front, maybe first try a thin (1 mm or thinner) spacer behind the cassette to increase the chain line at the rear? This assumes that the cassette lock ring is deep enough to securely engage the freehub and no clearance issue between the chain and the right chain stay after shifting the cassette to the right by 1 mm. At least it would be an inexpensive potential solution.
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Old 04-27-23, 06:56 PM
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Originally Posted by Koyote
Your post reminds me -- I forgot to mention that the rest of my drivetrain is Ultegra, as is yours. Works like a champ.

I had my bike built a week or two after GRX was announced, and the shop thought the 48-31 crankset would work better than the aftermarket crank (Praxis) that we'd been planning to use. So they built the bike with a placeholder Shimano 50-34 crankset (a pull-off from a new bike they'd sold), then installed the GRX crankset and FD when they became available after a few months. I noticed no difference in shifting performance, nor anything else. Which is why methinks the OP is a bit OCD about this.
OP here.... Can confirm, the OP is definitely a bit ocd about this! 😂

In all seriousness though, I think the 46/30 is best used as basically a 1x with the small ring as a bailout gear. My ideal setup would put the big ring dead center of the cassette. I've done this with good success on older bikes with square taper BBs. I know that's probably not doable with this newer tech. But right now the rings are set to the outside which is the opposite of this logic.

I appreciate all the comments of "you don't need to move the chainline, stay out of the big-big gears, etc". But that's not really what I'm asking here. Please indulge my OCD a little bit. I'm sure the current setup "works fine" but I also think if the crankset had a standard road chainline it will "work better".
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Old 04-27-23, 07:02 PM
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Originally Posted by maddog34
ID-wise.. as to that chainring... notice that the valley between each tooth is no longer symetrical? the rear wall is more vertical and the front wall of the valley is more laid over toward the front? that's wear.
Also note HOW the chain rollers seat in those valleys? the chain sets high in those valleys towards the exit off the bottom of the ring... A new large chainring might help eliminate most of that gap, since you say the chain is new... Mileage is less of a factor on any bike used off-pavement than visible wear... and all us online mechanics have to go by is the pics posted... Chain ring tooth wear is extrapolative.. the more wear there is, the faster it will wear due to less teeth being presented to the chain under load... the effective diameter of the chainring is reduced because of the wear... at some point the chain's sideplates begin hitting the chainring when the ring has a machined ridge like yours does.... all the wear increases "CHAIN NOISE", which is why you're wanting to alter the chainline, right? "Chain noise" is the chain slipping up and down in those tooth valleys under load, or rubbing against the der. cages, btw,,, I've seen some Tragically worn out chains in the past that made noise, but that chain is "new"....

Based on the pics and info provided, I advise trying a new large Chainring before you move Both chainrings.
Just Curious.. What brand/model/ # of speeds, chain is that? Peened pins, flat sideplates, no markings visible..

and i completely agree with the other responders that mentioned using the small ring more often.. it shows next to no use..
I see what you mean about the shape of the teeth on the big ring. Still though, 1000mi seems way too fast for this kind of wear, right? Maybe I'll try the "how far can you pull the chain off the chainring in the middle of the wrap" test, since it's a new chain. I'll try to get more pics of the chainring too. Perhaps the outside of the teeth are just worn in a funny way from riding in the big-big combo with the chainline a little wide? As I said in another post, my ideal setup would be to have the big ring near the center of the cassette, kind of like a 1x with the small ring functioning as a bailout gear. That's my motivation for this change, moreso than just straight up chain noise.

It is a Shimano CN-HG701 chain, by the way.
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