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Shimano GRX subcompact crankset and FD upgrade report

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Shimano GRX subcompact crankset and FD upgrade report

Old 08-16-19, 01:15 PM
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zpl
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Shimano GRX subcompact crankset and FD upgrade report

I knew within the first few rides that I was going to want to switch to a subcompact crank on my 2020 Trek Checkpoint ALR5, which comes stock with a 105 R7000 drivetrain and compact 50/34 crank. I've got a BB86.5 bottom bracket that I didn't want to fiddle with, so I waited for the new GRX components to become available.

BikeTiresDirect had my desired GRX 600 46/30 crank in 172.5mm available, as well as the (braze-on) GRX 810 front derailleur, so I jumped almost as soon as they arrived in stock and installed them last night on my bike (with a Dura-Ace FD braze-on to clamp-on adapter).




After my first commuting ride this morning, I can say so far so good! The lower gearing makes the big ring my primary ring most of the time now, and I only removed 1 link from the chain rather than 2 to make sure I didn't go too far when shortening the chain, since I'm likely to end up cross-chained in the big-big combo every so often.

I believe the GRX crank has a slightly wider q-factor than the 105, and I may now have enough room to reinstall my Wahoo cadence sensor on the back of the (non-drive) crank. Previously, that wasn't an option due to the tight clearance with the chainstay. However, one thing that surprised me is the ultra-narrow clearance between the chain and the drive-side crank when in the big chainring/smallest cog combo. There's barely a mm there, and I could no longer use one of those plastic protective boots that you can get for the tips of your crankset. This is no doubt due to the fact that the GRX crank and FD move your chainline outward 2.5mm.



Here's the final result:




If you're looking to do this upgrade, I found these YouTube videos to be very clear and helpful when it comes to crank replacement and setting up the new FD:

How to Remove & Install Shimano Cranks:
Shimano 105 R7000 Braze On Front Derailleur Fitting Guide:

Now go forth and climb great things!

Last edited by zpl; 08-16-19 at 01:19 PM.
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Old 08-16-19, 01:42 PM
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Good report, thanks!
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Old 08-16-19, 06:11 PM
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Agreed. Great post.

This is the first I've heard about anyone swapping cranks and FD from Shimano road to Shimano gravel. Congratulations.

The doily is a nice counterpoint to the gravel cranks too. Kudos on the photography.


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Old 08-18-19, 11:51 AM
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Thanks for the followup. I wish I had known about the GRX cranks when I redid my 2001 Ultegra triple 9spd to an 11 spd subcompact about 10 months ago.
Only 48/32 crank I could find under $200 was the FSA. GRX would have been a better and significantly cheaper choice.
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Old 08-18-19, 01:08 PM
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Originally Posted by sch View Post
Thanks for the followup. I wish I had known about the GRX cranks when I redid my 2001 Ultegra triple 9spd to an 11 spd subcompact about 10 months ago.
Only 48/32 crank I could find under $200 was the FSA. GRX would have been a better and significantly cheaper choice.
Donít kick yourself - grx was only announced a few months back and the components are just now trickling in. This thread is the first real-world report I know of someone getting their hands on grx.
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Old 09-11-19, 02:17 PM
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Thanks for posting. How do you determine whether you need to shorten the chain?
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Old 09-12-19, 09:55 AM
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It's been so long since I looked it up, I can't remember if the instructions come with the chain or the rear derailleur, but I typically wrap the (new) chain around the biggest cog on the cassette and the biggest chain ring and then add two links. That way, if you inadvertently shift into the "big-big" combination, your chain is long enough to handle it.

Mike
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Old 09-12-19, 11:05 AM
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In sizing a chain, I generally start with the small-small combination, and ensure I don't have any derailleur cage drag, and size to that. In doing so, you'll almost certainly have plenty of chain for the big-big combination. This seems to result in a little less chain tension (compared to a shorter chain) and my drivetrains tend to run a little smoother/quieter this way.

The approach Mike shared above will give you the shortest chain your drivetrain can handle. The approach I shared above will give you the longest chain your drivetrain can handle. Either one will work.
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Old 09-12-19, 11:44 AM
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Another data point: switched out a Shimano 50-34 crankset for a GRX Ultegra 48-31 model, and had to remove the Ultegra 8050 di2 FD and replace it with the GRX equivalent. The Crankset and FD are both offset, and apparently the new crankset wouldn't work properly with the old FD.

No problem running the 48-31 with an 11/34 cassette in an 8050 Ultegra RX RD, though, even though the setup exceeds it's max capacity by one tooth.
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Old 09-12-19, 12:27 PM
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Following thread. I just did a lot of research into the GRX line but pulled back at the last minute for now. Just to much to swap from my exiting glob based on a traditional Shimano 2x10 setup with the original road pull ratios (Tiagra 4600 and similar). I would have had to do the whole GRX line of brifters, FD, RD, and cranks. I still got my 46/30 but did it just with chainring swap and some chain links. Maybe later..

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Old 09-12-19, 03:54 PM
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Originally Posted by u235 View Post
Following thread. I just did a lot of research into the GRX line but pulled back at the last minute for now. Just to much to swap from my exiting glob based on a traditional Shimano 2x10 setup with the original road pull ratios (Tiagra 4600 and similar). I would have had to do the whole GRX line of brifters, FD, RD, and cranks. I still got my 46/30 but did it just with chainring swap and some chain links. Maybe later..
I am curious as to what crankset you are using to get to a 46/30 set up.
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Old 09-12-19, 06:16 PM
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Originally Posted by delbiker1 View Post
I am curious as to what crankset you are using to get to a 46/30 set up.
Existing FSA Omega. Originally 50/34 and swapped to FSA 46/30 (120/90BCD) rings for about $50.

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Old 09-12-19, 06:44 PM
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I am a little confused. How do you mount 120/90 BCD rings on a crank that is 110 BCD? Are you saying your Omega crank is 120/90 BCD?
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Old 09-12-19, 07:42 PM
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Originally Posted by delbiker1 View Post
I am a little confused. How do you mount 120/90 BCD rings on a crank that is 110 BCD? Are you saying your Omega crank is 120/90 BCD?
I thought all Omega were 120. I know mine are. The Gossamer series is 110.

Specific to the rings:
Full Speed Ahead FSA Pro Road Bicycle Chainring - 120x46T (30T Compatible) Black N11 WA068-370-0047003050
Full Speed Ahead FSA Omega Steel Road Bicycle Chainring - 90x30T Black N11 WB025-370-0050021140

FSA also has another 120 46 tooth ring that has a different shape made specifically to be paired with a 36 inner ring.

The cranks are FSA Omega Compact that came with 50/34 (just took them off last week). There is a FSA Omega Adventure crankset that comes with the 46/30. Same cranks as the Compact but with the above rings instead. I am using a CX70 FD and it works perfect.


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Old 09-13-19, 02:36 AM
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Thanks for the info, I did not know FSA Omega were available with 120 BCD. One of the reasons I like BikeForums, info to be learned from others experience.


Originally Posted by u235 View Post
I thought all Omega were 120. I know mine are. The Gossamer series is 110.

Specific to the rings:
Full Speed Ahead FSA Pro Road Bicycle Chainring - 120x46T (30T Compatible) Black N11 WA068-370-0047003050
Full Speed Ahead FSA Omega Steel Road Bicycle Chainring - 90x30T Black N11 WB025-370-0050021140

FSA also has another 120 46 tooth ring that has a different shape made specifically to be paired with a 36 inner ring.

The cranks are FSA Omega Compact that came with 50/34 (just took them off last week). There is a FSA Omega Adventure crankset that comes with the 46/30. Same cranks as the Compact but with the above rings instead. I am using a CX70 FD and it works perfect.

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