KLauwaet

I recently bought a new road bike and am planning to convert my old bike, a Trek Domane SL5 with a Shimano 105 11-speed groupset (Front: 50/34, Rear: 11-34), into a gravel bike.
Both the crankset and cassette are worn out and need replacing. I intend to use 38c gravel tires on it.

Could you advise on suitable replacements for the crankset and cassette? Also, is it possible to retain my current front and rear derailleurs?

Are there any other considerations I should keep in mind during this conversion?
Thanks in advance.

Troul 

are you planning on keep the drop bars on it? A dropper post might be of benefit.

Trav1s

You can stick with the 105 and replace the crank rings. As for cassette, the 11-34 used in the GRX series is the same as 105. A GRX rear derailleur has a clutch that reduces chain slap but that's not necessary. I found this interesting as I have been researching for a gravel build:
GRX400 = Tiagra
GRX600 = 105
GRX800 = Ultegra

grumpus

Seems to me that pretty much is a gravel bike already - I'd advise fitting the new tyres and seeing how it rides, if the worn out power train allows. If it's good then just replace those components with something similar. Otherwise you might consider converting to a 1x transmission, which will need a new rear derailleur along with the other parts.

shelbyfv

I'd get a GRX crank. They are reasonably priced and a straight swap. You may be able to use your existing 105 FD but it's trial and error. Again, GRX FDs are inexpensive. I'd probably get one just to avoid the possibility of having a do over. As pointed out above, your existing RD will work but the GRX has the clutch.

Trav1s

My reading says the respective GRX FD is needed as the GRX crank moves the rings 2.5mm outboard to aid with tire clearance. I don't know if there is enough adjustment in the 105 piece to make it work.

shelbyfv

That is correct. Sometimes a road FD will work, sometimes it won't, trial and error. Or just get the GRX and be done.