are there any visible physical differences between the 2? thinking of having a buddy pick some up from a friend and wanted to make sure they are indeed S5 rotors.

thanks

The bathtub in S4 is cast, and machined in S5 and S6.

thanks...but that means, what exactly?? is the surface smooth vs rough? or can u see an actual casting line?

the s4 is bumpy cause its just a raw casting, vs the s5+ machined chambers



mike