I have 10.5 inch wide, 19 inch rims in the back - they look great, but they were rubbing lightly when the suspension was compressed. I was able to have a couple things tweaked to eliminate the rubbing, but I would caution you against 11s
If you go any wider you have to have the correct offset..
I think 11" are just too much.. 10's are a stretch IMO because of the tires.
with 11" you will need a tire to fit other than a 275 30. If you go with a different tire size you speedo is going to be off, AND you will more than likely rub anyway..
Why go through all of that trouble.. IF your wheel get to the the edge o your fender as much as possible without rubbing, that's cosmetically the best set-up. Anything else is just too much.. sticking out for such a classy looking car.
The ultimate set-up is a 44 offset on a 20X9.5 rear and run toyo's or Nittos, or some other non squared tire and you will look perfect.
This site wont provide an answer to your question about how wide a wheel you can go, but it helps a lot with the tire size. Play with the site a litttle. You'll discover a bunch of tire/wheel size combinations that will work or wont work on our cars. Pay special attention to the "Overall Diameter". If you don't, thats when you start having rubbing issues. Not that the rubbing issues can't be addressed (i.e. rolling the fenders, etc.). Using too big an Overall Diameter tire-wheel combination will escalate (work and money wise) the simple changing wheels.
The site also will tell you the variance on the speedometer, if any, from the original size tire/wheel to whatever you want to tire wheel size you want to play with.
Oh, and if there is a variance greater than 3% on the speedo, it will give you a warning.
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