Hi I have a 2010 Mercedes e class rwd. It hasn’t been stock in years but I’ve been running 255/35/19 front and 275/35/19 rear. I recently went to 235/40/19 front and 285/35/19 rear. I love the ride so much better but I think it gave me a few weird shifts or maybe I imagined it. I was wondering if this is a large enough size to mess up the transmission of the car if I continue to drive with this setup. The wheel widths are 8.5 front and 9.5 rear if that helps.
No, as long as they’re the same size on both sides of the axle you aren’t going to have transmission problems with a larger tire.
You should go down on aspect ratio if you go up in width however, as going to 285/35 from 275/35 will increase overall diameter of the tire and your speedometer will be slightly less accurate.