Several on these forums are running 11-42 cassettes with 46/30 chainrings using a Shimano mid-cage Ultegra 8000 series rear derailleurs. This is what I'm running for bikepacking. A CS8000 XT mountain bike cassette is used with a 1.85 mm spacer behind it and a whole 116 link chain is required. Low is 19.5 gear inches.

The lowest gear combination you can get with GRX is going to be a 30 tooth ring in front and a 36 tooth sprocket in the rear for about 23 gear inches. That's pretty low but most touring and bikepacking guys like to have at least one gear in the teens.

No one really knows much about GRX other than what has been written as it hasn't really been seen on actual bikes being ridden yet.


-Tim-