the 160 has 160mm rotor (the shiny thing that spins is 6in) the 185 has 185mm rotor (the shiny thing that spins is about 7in)

the 185 is heavier but gives greater stopping power, also i've heard that with larger rotors you can have issues on a quick release set up, but to my knowlege thats only with the 203mm rotors (too much stopping power for xc lol) but thats just what i've been told