Shimano GRX400 RD 2x10 30-46 front with 11-42 cassette, anyone?

Hello! I do have a Cannondale Topstone 2 2021 Gravel Bike. From its original drivetrain configuration I did change 11-34 10speed cassette for a 11-40 10speed and it runs without issues - even chain crossing (not recommended). I was wondering about increasing cassette range to 11-42 10speed is possible. Does anyone have tried this configuration before? How it goes? Thanks!

I too have a Topstone, but mine came with the 11-speed gruppo.  I could not for the life of mme (my mechanic, I should say) get the 11-40 to work across the range, so I resorted to a XT rear derailleur and adapted the indexing with a Wold Tooth Tanpan.  While I don't cross chain, having going this route makes the system fail-safe.

 

Certainly, an 11-42 would work using this approach. 

OP:  You and I have the same setup, although mine is 11 speed.  I will try 11-42 once I wear out the cassette.  Two suggestions:  1) Be mindful of the choice of cassette, as regards the gap between the two largest cogs (as you re 10s).  2) Consider substituting a larger lower jockey wheel for the derailleur.  I've done this and it does help with taking up the excess chain slack in the higher gears, particularly before switching up to the larger chainring.  If you remember please let me know how it goes as I'll probably change cassette with the next chain change.  Good luck.

My dream setup might be possible: Shimano 2x12 with a 10-45.  I am going to start a new thread for this.