About to buy a new road bike so been looking at the PX RT57. Couple of things that I’m not sure on.

Firstly, will be running compact cranks (50/34)and a 11-28 cassette – I can use a mid length or short rear mech. Which one should I use? Presumably the short would be better suited.

Secondly is crank length. Been advised to run with 172.5mm. I run 175mm on the mtb but been told with compact that 172.5mm will be better. Seen similar stuff on Google but have no idea why!

crank length is nothing to do with the size of chainrings so who ever said that with a compact you are better with 172.5 is talking out their hoop for a start

50/34 11-28 is a max difference of 33

a road short has a 29 max on paper.

thus the mid is the better fit. A road short will work IF you never cross gears …. on a compact you will cross

Thanks trail rat.