I'm looking to pick up a set of Forgelines for my 997 C4S in 19x8.5 front and 19x12 rear with stock sized Pilot Sport Cups. Can anyone tell me the proper offsets to run these sizes? And am I better off with a 19x9 front wheel or is 8.5 better suited for this tire size?

 

What tire size? Are these for street or track?

 

235/35/19 front and 305/30/19 rear. They are for street and track but the car isn't driven on the street much.

 

My T4S has these tire sizes on the Carrera Sports, which have a 55mm front offset (8.5" rim) and an effective 60mm rear offset (11.5" rim). The actual wheel offset is 67mm (which fits narrow body cars), but the factory installs 17mm spacers on the rears to adapt the wheels to wide body. Have you checked to see if 305s fit properly on 12" rims (I know they are used on 11.5" rims).
FWIW, Champion recommends a 44mm offset for their 11.5" rear rims (on a wide body) to give a more aggressive stance.