Chainset replacement

[julianalston123!]

Will a shimano GRX RX600 30/46 fit ok to replace a shimano FC 6800 34/50. Will the front mech be OK?

Thanks

[scottm]

You need a GRX front mech, e.g. Shimano GRX FD-RX810 as the gravel chainsets have a greater Q-factor (2.5mm each side)

[531colin]

It may be possible to make an eccentric spacer, depending on the clamp size and frame tube size .
heres one I made to get a "MTB" front mech. to work on a chainset with "road" chainline. (the white stuff is double sided tape; I was running out of hands)

001 by 531colin, on Flickr

[Cyclothesist]

I wonder if you'd get away with keeping the road front mech? The hi and low stops plus the cable tension would all need to be tweaked but there's usually enough throw on a Shimano road FD to overshift the chain right off the big chain ring. The question is whether an extra 2.5mm is too far?
Disclaimer: I've never run a road FD on a gravel chainset. I have done a 1x to 2x conversion on a Tern that required a chainline of 51-52 mm to work. The road FD accommodated that fine.

[Brucey]

if it is possible to use spacers in the BB assembly it may be possible to move the whole crankset leftwards which may make things easier for the FD. When HT2 was still a new thing, they made MTN cups narrower than 'road' cups, thus affording the opportunity for chainline tweaks.