Shimano GRX and cross compatibility

Shimano GRX… a long time coming but finally something to get excited about…2/3 tiers of spec. 1x and 2x and even 10 speed options.

The downside being a lack of availability and according to official sources, little or no cross compatibility with existing road Shimano groupsets.

So, I’m currently running 2x11 105 on my CX/gravel bike, and there are a lot of owners out there running a similar set up.

We all know that you can usually get away a with 32T cassette and mid cage 105, even 34T (and possibly 36T on a really good day with an extra long B screw), but the limiting factor has always been that pesky 110bcd chainring and its 34T inner chainring limit.

Well, I’m not prepared to wait for the 11 speed chain set availability or pay a hefty premium, so gambled on the GRX FC-600 10 speed front chain ring in 46/30. I wasn’t prepared to buy a new front mech either just because of a 2.5mm chain line variation…

And as expected :wink: it works! Shifting is smooth and the chain runs freely with no rubbing of the front mech in any gear combination

As I mentioned above, the chainrings sit 2.5mm further out to accommodate wider tyres, which does make for even worse big/big cross chaining.

And finally, if you are thinking of fitting an aftermarket power meter, the left hand crank is scalloped on the inside which may well cause issues.

But any 105 upwards HT 2 crank will fit, I simply put my 105 crank with PM back on and everything is now working perfectly.

It’s always a pain to upgrade perfectly good components and whilst YMMV it seems like at least some components of Shimano GRX are good for mix and match.

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Do you have a 5800/6800 FD or an R7000/8000? If its the 5800 series, can you post a pic of the cable mounting arm with the cage in the outer most position? Mine already comes super close to touching the tire

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It’s a 5800 band on. I’ll get some pics up in the next day or so but I had no issues with a 700 x 38C tyre prior to moving the chainrings (and hence mech position) outwards by 2.5mm so I expect the clearance to have increased.

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The clearance actually decreases since the arm has to move inwards towards the tire even more than before to move the cage out 2.5mm further. Its a common problem hence the redesign on the r7/8000 series. I’m guessing that’s why the GRX cranksets are not technically compatible with the older series
https://forums.mtbr.com/cyclocross/front-der-tyre-rub-new-swiss-cross-1046846.html

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Ok, I’m with you. Sorry, I missed that you were specifically talking about the arm itself. I’ll take pics tomorrow and report back.

Edit: although your tyre size and chain stay length will mean that what works for me might not work for you. What tyre/bike combo are you running… schwalbe G-One 38c + ?

@redlude97 looks like it’s a product of your frame design, the back wheel must be tucked right into the seat tube. On mine the tyre/frame clearance will be an issue before I have to worry about the front mech.

image

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yea its mostly an issue on cross and road bikes with tires butted up against the seattube

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Am I getting this right, you have a 105 PM fitted to the 2x GRX crankset?

Yes, any HTII shimano crank will fit… Tiagra,105, dura ace, slx, xt etc

Perfect thanks very much, I’ll defo get the 2x GRX on my next bike then.

Hey Jonnyboy, hopefully this pings you a notification.

What’s your chain and driveside crank clearance looking like in the big ring and smallest cog on the back, I haven’t seen any other posts as in depth regarding the double chainset as this…

I’m running the 810 groupo on a surly cross check and it’s squeaky bum tight between the crank arm and the lower half of the chain running towards the rear mech!

The frame’s rear end is far from dead straight but I’m interested to see if is due to the outer chainring adjustment of +2.5mm and then the crank just sitting closer to the chainring.

Ciao

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I have the same setup on a GT Grade. In theory the pedal on the non drive side should be spaced outward by 2.5mm to keep the Q factor equal. The 105 front changer is not far off the max limit but works fine.

What’s your drive side crank and (lower) chain clearance like dude?

I’ll take a look, I don’t remember it being substantially different to the FSA crankset it replaced, no problems so far.

Shimano GRX 800-level components and 11-speed GRX 600-level components are compatible with current DURA-ACE, ULTEGRA, and 105 road groups.

Shimano GRX 400-level and 10-speed GRX 600-level components work great in conjunction with the 10-speed Tiagra road groupset.

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Good stuff as I am looking at swapping the FSA BB and Chainset on my Topstone Tiagra to the 10 speed GRX to (hopefully) allow me to use my hollow tech 2 crank power meter. I thought I was looking at front derailleur too at least.

sorry, just picked this up. will take a look later for you

Wondering if the 46 tooth GRX outer chainring will fit on the 105 5800 cranks? Need to find a 46t 5800 compatible chainring for junior racing

Hiya Marco

Found this on another website

Question 4:
Does the GRX series of cranks use the same 4-bolt chainring pattern as Dura-Ace 9050/9150 and Ultegra 8000/8050 series?

Dave: It is the same bolt pattern, but because of how the bigger chainrings are generally designed, they won’t physically match up to look pleasing aesthetically. However, the smaller chainrings being smaller (31T option etc), did require a differ BCD (bolt circle diameter) of 80mm to make everything work.

Alternatively you could try absolute black oval outer chainring or I do know there is an Ultegra 6800 46T outer chainring. That may well fit but I haven’t done any compatibility checking

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just looking for something compatible, dont really care about looks, ill have to look at the absolute black ones, couldnt find 6800 ones anywhere, thanks for the help

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