Using the R170 Encyclopedia...
the stock front wheels are 16x7 ET 37.
the stock rear wheels are 16x8 ET 30.
Using the fitment chart... Mercedes-Benz Fitting Chart and Wheel Fitment Guide | Alloy Wheels Direct
18x8 ET 31 is listed as an AMG front wheel. I have two 18x8 ET 30 wheels (1 mm difference) so I'm confident they will fit the front.
The offset calculator... Wheel Offset Calculator | Tiwing.com
says I'll have 6mm less inner clearance and the wheels will extend outwards an additional 20 mm as compared to the stock wheels.
Again using the fitment chart...
18x9 ET 35 is listed as an AMG rear wheel. I have two 18x9 ET 39 wheels (4 mm difference). I'm guessing that will be good too.
The offset calculator says I'll have 22 mm less inner clearance and the wheels will extend outward an extra 4 mm as compared to the stock.
Has anyone used 18x9 ET 39 (or similar) on the back of their R170?