im setting up a ss 38t cog up front with a 12-32 cassette in back, 8 speed.
what size rear derailleur do i need, im guessing 8 speed but what size cage is best etc. also what size chain for this setup. im hoping i dont need a chain guide cos they cost a bomb! but if i do any cheap good ones that could be recomended would be class. cheers folks

You can also run a 9 speed mech on that. I would run a medium cage (GS denoted) MTB mech like an SLX or XT but I am sure some would say run a short (SS denoted) road mech like a Tiagra or 105.

I run a 26-38 and 12-32 on tmy bike, with a SRAM super short X9. Also 8/16 speed. All works fine.

For Shimano mechs, either a medium MTB or short cage road (8 or 9 speed) will be fine.

great thanks so do i run a 8 speed chain someone before told me you go a size up or down i cant remember.