I have a Trek Crossrip with Shimano Claris. Front mech is 3 x 8 with 50 / 38 / 30 teeth. I would like to fit a Shimano Alivio chain set with 48 / 36 / 26 teeth, would this be compatible ??
You can most likely fit a MTB triple crank, but it won't really be compatible because MTB triple drivetrains use a chainline of 50mm, whereas road triples use 45mm.
Basically if you fit a MTB triple crank the chainrings will be 5mm too far outboard relative to the cassette sprockets which will make cross-chaining from large chainring to large sprocket very bad, likely give you shifting problems and front derailleur chain-rub issues.