Wheels will be 20x10 n the rear with 20mm offset. I want G-Force TA tires and tehy dont have them in 275/30, only 285/30. I dont want to make any other mods, and I frequently have 4 adultsw in the car. I live in Arizona so teh roads are in very good shape, no pot holes.

 

I had 20"x 10" - 275/35 in the rear on my 545i.

To avoid rubbing with loaded car you will need to roll the rear fenders.

 

Careful: Alexbr has an M5 which rides significantly higher than a 550i sport. I have 285/30 19 rear tires on my 550 sport and they don't rub, but I didn't get the 285/35 19s from the M5 because I heard they would rub. So I'd guess that your 20s in that size would rub. For what its worth, I hate the ride with these tires. Its not that its harsh, its that the car is very squirmy with such a wide tire and small sidewall. It rides like a Vette. Step on the gas and the rear moves around. Same thing changing lanes on the highway...feels unstable. Search the forum for info. on this. It sounds crazy but if you want big wheels, try to keep a 35-40 profile and consider narrower rear tires. If you got springs that allowed you to use 265/40 20 rears, I have to believe you would be much happier with the handling of the car than using the 285/30/20s. The wide tire with ultra low profile follows every crack, line and imperfection in the road.

Good luck.

DRP

 

I was talking about my 545i that had 20"'s