GRX 2x chain length

I’m rather behind the times, but I’ve always sized my chain using the big ring/big cog +2 rivets approach. My main bike is still 3×10 with an 11-36 cassette & this has been fine for years.

When I built up my gravel bike (with a GRX400 2x setup) the instructions for sizing the chain said to use the big ring/big cog method, but add 4-6 links, so I used this approach.

I assumed at the time that this was grx specific but it now seems to be Shimano’s default approach – https://mtb.shimano.com/stories/determine-chain-length

The Park Tools website still lists the ‘count on 2 rivets’ approach but goes on to add that single ring set ups with cassettes with 42 tooth or bigger cogs need 4-6 links.

I don’t know if Shimano are assuming that everyone rides single ring set ups, but I think I might have cut my chain too long on the gravel bike. with 2x cranks and an 11-36 cassette should I just be adding 2 rivets to the zero point?

I set up a GRX 2*10speed bike a few months ago. I read Shimano’s new setup method as put the chain on small-small, routed through both derailleurs, with just enough length so the rear derailleur is lightly tensioned. That’s working well.

It’s really just modern 1x rear mechs with the massively offset upper jockey wheel that need the 4-6 links.

I thought +2 was fine upto 11 speed. The +4 to 6 is a Shimano 12 speed thing. Only time I’ve ever used it is GRX 1×12

The old ‘+2 links’ advice comes from the time (not all that long ago) when where the difference between (double) chainrings was less, and the Cassette range was narrower, the GRX rear mech will take up more slack than an older Ultegra would have

It’s probably better to follow the shimano advice and go long (+6 links) and see how it goes, take a pair out if there’s too much slack in ‘small-small’, it’s always easier to remove links than add them back in…

Ah, then I’ve been a bit premature as I’ve gone with the Park Tools site & 2 rivets. It seems to work & nothing breaks in big/big but I aught to change back if I’m going to damage something.

I’ll have a couple of rides at some point & see how I get on

You will be fine. I went a tad short by accident on 2x GRX and it’s working well. You shouldn’t really ever be in big/big (though accidents happen and modern drivetrains are good with it); avoid cross chaining if you hear it grinding and I can’t really see the harm.

Perhaps I should just stick with Shimano’s instructions. Interestingly they seem to cover a range of mechs. & make no reference to the number of cogs or rings.

Google’s AI decided to chip in when I was searching & suggests big ring, big cog + 2 inches.

For reference:

46/30 GRX chainset, 11-34T cassette, GRX mechs, 440mm chainstay = 116 links (which is a pain because sale chains are often 2 links shorter than this!)