I just bought a set of 3.6 turbo Gemballa's. The front fit fine, but the rear right is scrapping the inner wheel. I have an America Roadster with the rear wheel offset being 55mm and 17x9 for the size. The new wheels are 18x11 and 65mm. The left rear wheels is fine and the right rear scraps slightly. Would any know what spacer I need. The rear fender still have space. Thank you all in advance.

 

I would guess the scraping is the oil line so I would stop moving asap. The Turbo 3.6 wheels had an offset of 61mm on the Turbo so I am guessing that is what you will need (at a minimum). You might want to start with a 6-7mm spacer and see if that works. If not, I believe the next up would be a 13-14mm (?). Good luck.

 

After the wheels were installed I took the car on a test run. I traveled roughly 10 ft on a slow roll. The whole time the rear right wheel was scraping the lower control arm. I will try an 15-20mm spacer. I will post the results.

 

You are going to need a 35 mm spacer on each rear wheel to provide the static and dynamic clearance provided as standard. I am sure this is going to take you to rubbing on the fender.
Please be advised that these wheels are far too wide for any 964 except the ROW 964 Turbo 3.6, 964 RS 3.8 and 964 RSR which had a specially designed rear suspension and geometry to take such wheels. Not even the US version of the Turbo 3.6 was designed for such width wheels. Gemballa wheels are designed for the ROW version of the Turbo 3.6.
I honestly do not believe you will overcome this issue. Move them away from the inner arch and you hit the fender. This gets expensive especially if you trash the tyres everytime you go over a bumb.
Ciao,
Adrian
964C4