Just gazing longingly in the window of our local bike shop with a bike setup with latest 12 speed 1x GRX, looked like a 10-51 cassette although the rear mech was surprisingly short.Â
Anyway, the chainring was definitely a 1x chainring, but it looked as if it was almost in line with the smallest sprocket! Logic would suggest (to me) that you'd want it lined up with the middle of the cassette but clearly Shimano are going to know what they're doing.
I'd seen comments on here before that the chainline wasn't very good. On my CX bike I run 1x GRX but an older vintage with a 2x chainset and offset Garbaruk chainring (I think 5mm) and it lines up fairly nicely with the middle sprockets. Still a bit rumbly in the absolute lowest gear. I'm considering a next gravel bike which I can use for CX racing also, something like a Giant TCX, and it would likely be 1x.
What's it like to ride?
I think it depends on:
Chainring offset, Shimano use two chainlines?
Chainring Size
Chainstay length
My Top fuel isn't particularly nice in the biggest cog, as it has the extra wide chainline, but being as the intention isn't to be in that gear that often it shouldn't be a big deal, definitely can feel it, i swear dropping down a cog is more efficient đŸ˜€ (at least psychologically)
That sounds odd. I have a mtb chainset on a drop bar bike with a 12 speed shimano rear  cassette and grx derailleur. I think the chainset is 52mm chain line. The rear wheel is 142mm (not boost). As you might expect my chain ring is a touch too far out board. But it’s still broadly mid cassette. The grx chainline is 2mm further in board and would be better.Â
GRX 1x cranks are 49.7mm CL. That's basically a middle ring position from the days of triples and 135mm QR rear hubs.
That's basically a middle ring position from the days of triples and 135mm QR rear hubs.
GRX 2x is 47mm, so I guess the 1x sits exactly where the 2x big ring would go? That's not as bad as it appeared through the shop window then, I occasionally stray into big ring and biggest sprocket on my 2x setup and it's useable at least.
So there's no compensation for wider OLDs? I.e. the chainring will effectively move closer to the biggest sprockets as the hub gets wider?
Yes GRX chain line is crap, it's no where near the middle of the cassette with a definite bias towards the higher gears. You can improve with a garabuk ring or chain line spacers. If you don't need the wide clearance road width cranks offer a better chain line. I noticed the increased noise immediately when I swap from Easton road cranks to a GRX cranks.
GRX 2x is 47mm, so I guess the 1x sits exactly where the 2x big ring would go?
1x is a 2x crank with only one ring fitted (though that ring might have a little offset in it compared to the 2x ring).
I think jameso is mixing apples and pears. Road triple was 45mm (Shimano) while MTB triple was wider at 47.5mm (Shimano preferred value).
I've GRX 11 speed on my Digger and it's been awesome for last few years. It hasn't missed a beat even when covered in mud. I changed from the original 40 tooth chainring a year ago to a Wolf Tooth eliptical 38 and it's still rock solid.Â
As mentioned above, the chain line does seem to favour the harder gears, but even though most of my gravel riding is XC MTB, the easier gears are still wearing well and I've never had a problem.
Got 38-11/51 11speed on my bike with std GRX crank and rear mech. Never had a problem with chain drop....in fact I don't think it's ever come off! And normal wear for a drivetrain that spends 75% of it's life either wet, muddy and mostly both.
Ok, am re-assured, clearly an optical illusion or something that made it look like the single ring was in line with the 11th sprocket!
I think for less mountainous gravel rides and winter CX, something like a Giant TCX with a 10-45 cassette and swapping between 38 and 40t chainrings depending on circumstances could be ideal, maybe even a smaller cassette and the shorter cage GRX mech for CX duties.
Time to get saving 😎