What Size Conduit for 4AWG
Upsizing makes your life easier

Since I doubt you have a truck loaded with nothing but pulling tools, you're better off upsizing the conduit to make your pull easier.  Get some 2" or even 3" schedule 80 -- you'll be quite happy you did!  (It also means you'll have room to put fatter wires down the pipe later if you want MOAR POWAH in the garage for some reason or another.)