Hi
Eclass w212 2010 standard tyre size is front:245/40/18 and rear:265/35/18. The side walls look too small and ride is a bit too stiff for a Mercedes. I was thinking of increasing the side walls slightly to 235/45/18 & 265/40/18... I think they will look better as the side walls front and back will be the same and overall diameter will also be the same (currently on stock tyres there is a slight difference!!) see below.

anyone tried this, and will they fit??

 

The tires should fit, but you are not telling anything about rims?
With rear you are closing the clearances, so proper match of ET can be crucial.
Have to prize you for doing your homework before starting the topic, but tires are manufactured with very loose tolerances and generic calculator can come with huge errors.
Go to tire manufacturer site and compare rpm or rpkm of the tires you like.

 

Make sure you are running proper pressures. On my 2011 W212 with sport package, the pressures in the the door frame turned out to be for max loading. Normal (and max) load pressures were listed on the fuel door that I had not even noticed even after 3 years of ownership. Derp. I had been following the door jam which was like 33F/42R (PSI) but normal load is actually 30F/35R. It softened the ride noticeably (until I went to 19s with new springs which killed everything) and was quieter as well.

 

I know it's been a while, did you change the tires?

 

Did the 235/45/18 fit?
If so, was there any rubbing issues?

 

I Had 275/30/19 on mine, Runs without problems