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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 04-27-23, 07:03 PM
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I probably use the 30T much more than I am "supposed to", but if you wear that one out, it is fairly cheap to replace. Having said that, you can replace the whole thing for $150.

If you want a 46/30 without the increased chainline offset, get a White Industries crankset. I have one of those on another bike. They are well made. You can get 30mm spindle or square taper. You can also get whatever size rings you want. However, plan to spend a little more than $150.

When you wear out a chainring, you will know it. There is zero ambiguity. The chain will skip all over the place until you shift to the other chainring. Also, you can pull on the chain wrapped around the worn chainring, and see lots of daylight come through the gaps.
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Old 04-27-23, 07:07 PM
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Originally Posted by 79pmooney
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.)
Thanks for this info!! I think I understand what you mean about needing a tight fitting support tube between the holes in the crank and chainring. I don't know if it'll work for this GRX crank though, as both rings mount from the inside on separate sets of bolts, similar to how the 74BCD holes work on an old triple. The rings are just clamped up against the spider, and there are no nuts.

I'd assume the holes in the rings are just big enough for the M8x0.75 chainring bolts (I need to pull them off and measure). I don't think the bolts provide any support besides clamping force though? So that's why I'm a little cautious to just throw spacers in there, it sounds like things might creak and wear our quickly?
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Old 04-27-23, 07:11 PM
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Originally Posted by xg5a
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".
You seem committed to this path so please check back and let us know how it turns out.
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Old 04-27-23, 07:11 PM
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Originally Posted by Polaris OBark
I probably use the 30T much more than I am "supposed to", but if you wear that one out, it is fairly cheap to replace. Having said that, you can replace the whole thing for $150.

If you want a 46/30 without the increased chainline offset, get a White Industries crankset. I have one of those on another bike. They are well made. You can get 30mm spindle or square taper. You can also get whatever size rings you want. However, plan to spend a little more than $150.

When you wear out a chainring, you will know it. There is zero ambiguity. The chain will skip all over the place until you shift to the other chainring. Also, you can pull on the chain wrapped around the worn chainring, and see lots of daylight come through the gaps.
I'm not super versed in BB standards besides square taper... Will a 30mm spindle fit on a bike with an English threaded BB shell?

FSA's newest generation gossamer crank also comes in 46/30 and I think might have a road chainline. Not 100% sure though. But then theres a version without a spider that has the GRX chainline.

Sugino OX2-901 appears to have a 46/30 in a road chainline, but for a ton of money. (Too bad)

On my current chainrings, the test you suggest is exactly what I'm going to try!
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Old 04-27-23, 07:12 PM
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Originally Posted by shelbyfv
You seem committed to this path so please check back and let us know how it turns out.
I will. To be honest, I also just like experimenting with bike parts, and I want to know how it will turn out!
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Old 04-27-23, 08:42 PM
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A 30 mm will fit a BSA BB shell, as long as you don't have a Di2 wire in there (ask me how I know).
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Old 04-27-23, 09:12 PM
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Originally Posted by xg5a
To be honest, I also just like experimenting with bike parts, and I want to know how it will turn out!
If you know how it will turn out, it's not experimenting.
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Old 04-29-23, 08:24 AM
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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 had a chance today to look at the chainring condition more. Since I have a new chain, I tried the "pull the chain off of the chainring in the middle of the wrap" test. The chain only pulls away about have a rivet diameter. I think that seems good? But I do see what you're saying about the teeth being hook shaped. I looked in detail and some teeth are definitely more hooked than others. I wonder if part of the effect is that the back edge of the tops of some teeth are worn down from cross-chaining? Looking at the shimano official picture of the chainring when new, (which you can hover over to zoom), the teeth do actually look hook-shaped. So, maybe this is just how the ring is supposed to look, rather than being very worn?



Lots of pictures of the chainrings below:







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Old 04-29-23, 11:19 AM
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thanks for the better pics...

Note to self: Apparently, Shimano is now designing and selling pre-worn chainrings.

I've seen this shape used on the Small cogs in cassettes, but had never noted it on a large chainring.

have you physically checked the chainline with a straight edge? i use an 24" combi-ruler. for this check.
is the mid-side of the small ring aligned with the middle of the cassette's 6th gear? 2mm will move the line one gear, almost... each gear is @ 2.18mm on an 11 sp. cassette.
i'm convinced it's more of a "rider's preference and style" thing than an actual chainline issue.

let us know how the new hardware works out.

Last edited by maddog34; 04-29-23 at 12:03 PM.
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Old 04-29-23, 11:38 AM
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Originally Posted by maddog34
PS.. that big ring is THRASHED... the chain, also. you got your money's worth outta them,.
That sure had me concerned, happy to hear different.
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Old 04-29-23, 12:01 PM
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Originally Posted by shelbyfv
That sure had me concerned, happy to hear different.
looks like the old chain rounded the tips off the teeth, and was probably the source of the noise concerns too... but actual tooth valley wear is minimal when the now much better images are compared to a new Chainring pic.

those early pics made a new chain and low-wear ring look tragic.
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Old 04-29-23, 02:40 PM
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Originally Posted by maddog34
thanks for the better pics...

Note to self: Apparently, Shimano is now designing and selling pre-worn chainrings.

I've seen this shape used on the Small cogs in cassettes, but had never noted it on a large chainring.

have you physically checked the chainline with a straight edge? i use an 24" combi-ruler. for this check.
is the mid-side of the small ring aligned with the middle of the cassette's 6th gear? 2mm will move the line one gear, almost... each gear is @ 2.18mm on an 11 sp. cassette.
i'm convinced it's more of a "rider's preference and style" thing than an actual chainline issue.

let us know how the new hardware works out.
Don't know where you are getting the 2.18mm number from, (width of the sprocket maybe?). A 2mm move of the chainline will be closer to 1/2 of a distance between cassette gears.

Even the OPs effort to get a 3mm change will have very little effect on the alignment, maybe a very small amount in the big/big combo.
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Old 04-29-23, 02:55 PM
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Originally Posted by maddog34
thanks for the better pics...

Note to self: Apparently, Shimano is now designing and selling pre-worn chainrings.

I've seen this shape used on the Small cogs in cassettes, but had never noted it on a large chainring.

have you physically checked the chainline with a straight edge? i use an 24" combi-ruler. for this check.
is the mid-side of the small ring aligned with the middle of the cassette's 6th gear? 2mm will move the line one gear, almost... each gear is @ 2.18mm on an 11 sp. cassette.
i'm convinced it's more of a "rider's preference and style" thing than an actual chainline issue.

let us know how the new hardware works out.
A closer look at the chainring was very enlightening for me too. I'm glad I'm not feeding a nice new chain to a worn out ring.

So right now, the big ring is aligned with the third from smallest cog. I'm actually thinking of trying something with 4mm spacers, so that would move the big ring almost to the 5th smallest ring. Could be good, or its going to creak and not work, we'll see. Haven't had a chance to actually put it together yet though.

Oh, and reading on another thread, somebody posted some specs that Shimano provides for frame manufacturers in terms of when you can use a GRX crank with otherwise "standard" road chainline parts. The minimum chainstay length was 415mm, which is exactly how long they are on this bike. (Chainstay length would affect the actual angle of the chain coming off of the cogs for a given front/rear chainline mismatch).

So on one hand, everyone is technically correct here when saying that I don't need to move anything. But also, I think the system can work better by following the old rule of thumb from the square taper days, to get the chainrings in as close to the frame as possible.
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Old 04-29-23, 03:08 PM
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Originally Posted by KCT1986
Don't know where you are getting the 2.18mm number from, (width of the sprocket maybe?). A 2mm move of the chainline will be closer to 1/2 of a distance between cassette gears.

Even the OPs effort to get a 3mm change will have very little effect on the alignment, maybe a very small amount in the big/big combo.
oopsy.. that's the SPACER thickness between the cogs.... busy day... the sun finally came out in the Willamette Valley.

Measure your 11 sp. cassette and post the outer face to outer face distance, ok? i don't see one here right now... lots of 7, 8, 9,10 sp, and i'm finishing up a 6sp right now....... no 11s

to guess, i'd say 3.8mm or so per cog change....

and i agree about the futility of the project.
look at the big ring's wear patternthough...the bike is being used in the big front/bigger than middle rear config.mostly... it';s a rider preference thing...he's trying to suit the rider (his wife) and reduce wear...
a happy wife makes for a happy life.

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Old 04-29-23, 03:27 PM
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Interesting that Shimano specifies a 415 minimum chainstay. My Topstone has 435 which I suppose is more forgiving, though still the big ring is aligned with the third smallest, as I mentioned earlier. FWIW, my drivetrain was disappointingly noisy the first half dozen rides. Finally I thought to lube the chain. I used some wax lube that was handy. That helped so I then used some sho-nuff oily lube. What a difference, duh. I've never before had a new chain that wasn't lubed well enough to run for a few hundred miles out of the box.
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Old 04-29-23, 03:46 PM
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Originally Posted by xg5a
A closer look at the chainring was very enlightening for me too. I'm glad I'm not feeding a nice new chain to a worn out ring.

So right now, the big ring is aligned with the third from smallest cog. I'm actually thinking of trying something with 4mm spacers, so that would move the big ring almost to the 5th smallest ring. Could be good, or its going to creak and not work, we'll see. Haven't had a chance to actually put it together yet though.

Oh, and reading on another thread, somebody posted some specs that Shimano provides for frame manufacturers in terms of when you can use a GRX crank with otherwise "standard" road chainline parts. The minimum chainstay length was 415mm, which is exactly how long they are on this bike. (Chainstay length would affect the actual angle of the chain coming off of the cogs for a given front/rear chainline mismatch).

So on one hand, everyone is technically correct here when saying that I don't need to move anything. But also, I think the system can work better by following the old rule of thumb from the square taper days, to get the chainrings in as close to the frame as possible.
my apologies.. i was too busy when i quoted that "2.18mm" .. that is the SPACERS between the cogs! the actual Gear change distance is more like 3.8mm, i'd guess.. i have no 11sp. here to measure right now... could you measure your cassette accurately, for future reference-sake? outer face to outer face on any adjacent gears...

as to the "aligned to the 3rd smallest cog" thing.. wow.. that is not good... you are heading in the right direction, mr. xg5a!
all doubts retracted!

i wonder... what's the rear spacing on your frame? and could GRX drivetrains be meant for only 142mm rear dropout frames? other narrower applications being a compromise situation? hmmmmm.....
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Old 04-29-23, 04:55 PM
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Originally Posted by maddog34
as to the "aligned to the 3rd smallest cog" thing.. wow.. that is not good...
I disagree. For a double that seems to be exactly where the big ring should align. I too am curious as to the rear spacing and I expect you are correct that GRX was designed with 142 in mind.
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Old 04-29-23, 06:45 PM
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Originally Posted by shelbyfv
I disagree. For a double that seems to be exactly where the big ring should align. I too am curious as to the rear spacing and I expect you are correct that GRX was designed with 142 in mind.
the 6th cog is the midline of an 11sp. cassette... wouldn't logic dictate that the chainrings of a double would be aligned to either side of that cog, equal distance? I always try to align a mid ring of a triple on the #5 cog of a 9 sp, etc...

or could shimano be "playing the odds" on chainlines, hoping that the biggest cogs get used far less often? i tend to run in the MID cogs most around here...small cogs are pushed less hard, big cogs see higher loads when i hit a climb.......
i guess i'm not prone to gambling.

and consider that xg5a's wife is using the small ring as a bailout only.. The chainline shift will align the small ring with the big rear cogs better too... win/win, eh?

i saw about 4.5mm, ring to ring, on my fuji 2x10 tiagra group, and up to about 6mm on some mtb triples on the shelves.. hard to get a quick read on chainrings due to ramps and such...

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Old 04-29-23, 07:29 PM
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Originally Posted by shelbyfv
Interesting that Shimano specifies a 415 minimum chainstay. My Topstone has 435 which I suppose is more forgiving, though still the big ring is aligned with the third smallest, as I mentioned earlier. FWIW, my drivetrain was disappointingly noisy the first half dozen rides. Finally I thought to lube the chain. I used some wax lube that was handy. That helped so I then used some sho-nuff oily lube. What a difference, duh. I've never before had a new chain that wasn't lubed well enough to run for a few hundred miles out of the box.
Don't forget, what really matters is the ANGLE that the chain comes off of the cogs. The exact alignment between chainrings and cogs only matters indirectly. For instance, imagine a bike with super long chainstay, like double the length of a normal bike...you could cross chain at will and the chain "angle" would stay at almost 0, perfectly straight.

So that's why your topstone with longer chainstays will be more tolerant than my synapse with shorter chainstays, with an equivalent "mismatch" between the chainrings and the cogs. And that's why Shimano has the 415mm limit, shorter than that and cross chaining would create a horribly large chain angle.

Originally Posted by maddog34
my apologies.. i was too busy when i quoted that "2.18mm" .. that is the SPACERS between the cogs! the actual Gear change distance is more like 3.8mm, i'd guess.. i have no 11sp. here to measure right now... could you measure your cassette accurately, for future reference-sake? outer face to outer face on any adjacent gears...

as to the "aligned to the 3rd smallest cog" thing.. wow.. that is not good... you are heading in the right direction, mr. xg5a!
all doubts retracted!

i wonder... what's the rear spacing on your frame? and could GRX drivetrains be meant for only 142mm rear dropout frames? other narrower applications being a compromise situation? hmmmmm.....
Originally Posted by maddog34
the 6th cog is the midline of an 11sp. cassette... wouldn't logic dictate that the chainrings of a double would be aligned to either side of that cog, equal distance? I always try to align a mid ring of a triple on the #5 cog of a 9 sp, etc... or could shimano be "playing the odds" on chainlines, hoping that the biggest cogs get used far less often? i tend to run in the MID cogs most around here...small cogs are pushed less hard, big cogs see higher loads when i hit a climb.......i guess i'm not prone to gambling. and consider that xg5a's wife is using the small ring as a bailout only.. The chainline shift will align the small ring with the big rear cogs better too... win/win, eh? i saw about 4.5mm, ring to ring, on my fuji 2x10 tiagra group, and up to about 6mm on some mtb triples on the shelves.. hard to get a quick read on chainrings due to ramps and such...
I will measure the cassette spacing tomorrow and post on here. (Edit: some googling indicates 3.74 mm (road), or 3.9 mm (MTB)). The frame has standard 142mm thru axle spacing. The thing is, GRX drivetrains are designed for gravel bikes with longer chainstays.

Here's how I see the design logic by Shimano. Road bikes have a "standard" chainline and 142mm spacing (which is really the same as 135mm QR spacing). And that all works fine, the chainrings are aligned with the middle of the cassette, etc. For the GRX parts, Shimano assumes the user might want to run wide tires for gravel, so the chainline has to move out at the crank to avoid interference with the tire. Rear spacing stays at 142mm but Shimano assumes it'll be ok because the gravel bike will also have long chainstays. So having the big ring sitting so far out results in not a horrible a chain angle.

Our logic with setting my wife up on the 30/46 was that, first off neither of us are super strong riders. Where we live (north NJ), we have lots of short, steep hills and relatively flat riding otherwise. So she really wanted that 30/34 (below 1:1) low gear to get up the steep hills. 30/46 is the only double crank factory option to get that. We could improvise something, but I didn't think a 30t small ring would work well paired with, say, a 50t big ring.

With true gravel riding (which my wife and I don't do) I'm sure you'd use the 46t and the 30t rings both quite a lot. Whereas using this crank on the road, the 46 gets used predominantly and the 30t is a bailout. I think that's the price of having a 30t small ring on a double. To be fair, she still doesn't use the 11, 12, and 13t cogs (neither do I) so the bike has plenty of gear range. It's just a matter of which ring for most of the terrain around here. Hope that all makes sense?

At the end of your 2nd post I quoted here, are you referring to the spacing between chainrings? I'm working on this project and also a tandem crank replacement, so I've been measuring a lot of cranks. I'm getting 8mm center to center spacing between chainrings across the board, does that seem right?

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Old 04-29-23, 07:57 PM
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Originally Posted by xg5a
Don't forget, what really matters is the ANGLE that the chain comes off of the cogs. The exact alignment between chainrings and cogs only matters indirectly. For instance, imagine a bike with super long chainstay, like double the length of a normal bike...you could cross chain at will and the chain "angle" would stay at almost 0, perfectly straight.

So that's why your topstone with longer chainstays will be more tolerant than my synapse with shorter chainstays, with an equivalent "mismatch" between the chainrings and the cogs. And that's why Shimano has the 415mm limit, shorter than that and cross chaining would create a horribly large chain angle.





I will measure the cassette spacing tomorrow and post on here. (Edit: some googling indicates 3.74 mm (road), or 3.9 mm (MTB)). The frame has standard 142mm thru axle spacing. The thing is, GRX drivetrains are designed for gravel bikes with longer chainstays.

Here's how I see the design logic by Shimano. Road bikes have a "standard" chainline and 142mm spacing (which is really the same as 135mm QR spacing). And that all works fine, the chainrings are aligned with the middle of the cassette, etc. For the GRX parts, Shimano assumes the user might want to run wide tires for gravel, so the chainline has to move out at the crank to avoid interference with the tire. Rear spacing stays at 142mm but Shimano assumes it'll be ok because the gravel bike will also have long chainstays. So having the big ring sitting so far out results in not a horrible a chain angle.

Our logic with setting my wife up on the 30/46 was that, first off neither of us are super strong riders. Where we live (north NJ), we have lots of short, steep hills and relatively flat riding otherwise. So she really wanted that 30/34 (below 1:1) low gear to get up the steep hills. 30/46 is the only double crank factory option to get that. We could improvise something, but I didn't think a 30t small ring would work well paired with, say, a 50t big ring.

With true gravel riding (which my wife and I don't do) I'm sure you'd use the 46t and the 30t rings both quite a lot. Whereas using this crank on the road, the 46 gets used predominantly and the 30t is a bailout. I think that's the price of having a 30t small ring on a double. To be fair, she still doesn't use the 11, 12, and 13t cogs (neither do I) so the bike has plenty of gear range. It's just a matter of which ring for most of the terrain around here. Hope that all makes sense?

At the end of your 2nd post I quoted here, are you referring to the spacing between chainrings? I'm working on this project and also a tandem crank replacement, so I've been measuring a lot of cranks. I'm getting 8mm center to center spacing between chainrings across the board, does that seem right?
I have a REALLY old Sugino Impel crankset on a bike on my stand right now... 7mm ring to ring... the rings have exactly ZERO Ramps on them, making a quick measurement easy and accurate... 7mm.. this thing is a 6-7 speed era bike... still equipped for 3x7sp.

Last edited by maddog34; 04-29-23 at 08:08 PM.
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Old 04-29-23, 09:30 PM
  #46  
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Originally Posted by shelbyfv
I disagree. For a double that seems to be exactly where the big ring should align. I too am curious as to the rear spacing and I expect you are correct that GRX was designed with 142 in mind.
It is, and it is exactly the same spacing as 135mm QR.
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Old 04-30-23, 09:00 AM
  #47  
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I have found the perfect solution for the OP:

Takagi Forged Tourney AD Triple Crankset 50/46/30
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Old 04-30-23, 09:27 AM
  #48  
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unfortunately Shimano options for GRX big ring are fairly limited

a simple solution is to use the small ring more - if not majority of the time

many ride on the level almost exclusively with a 30t / 31t front ring (and similar) with little issue
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Old 04-30-23, 01:59 PM
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Originally Posted by Polaris OBark
I have found the perfect solution for the OP:

Takagi Forged Tourney AD Triple Crankset 50/46/30
Very cool except for the square taper and totally different aesthetic from the rest of the bike. I do like the look of old components though, not gonna lie! And half-step gearing would be SO much easier to ride with STI shifters compared to downtube shifters. Too bad triple STI shifters are dead.
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Old 04-30-23, 02:36 PM
  #50  
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Originally Posted by Polaris OBark
I have found the perfect solution for the OP:

Takagi Forged Tourney AD Triple Crankset 50/46/30
I don't get the half step between the 50T and 46T chain rings. What is the shifting philosophy?
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