Randy1911

I have a 2015 s550 4matic and am looking for as much side wall possible for a 20 inch set up. With an 8.5 front the widest tire you can use is a 255/40/20 but it may not fit the car in which I dont know. The same with the rear a 9.5 set up the biggest you can use on that rim is 275/35/20 but I dont know if it fits the car. I know most are running 245/40/20 fronts and 275/40/20 rears but has anyone tried different.

Just an fyi 255/40/20 fronts and 285/35/20 is just a 17% difference in which is only a quarter of an inch smaller than the 19" set up which is why Im trying to push the limits of the fit.

superpop

Should be fine after looking at calcs for both sizes. It is basically a 1% increase in overall height. The big difference is that you will have a lot more tire hanging over the edge of the rim versus the standard fitment. Overall the bigger size adds about 2MM to the outer offset meaning the tire sticks out about 2MM further. Folks run 10MM spacers on these cars all the time with the stock 43MM offset.

jenz

Head to 1010 tires offset calculator to help run the math; I run the following with no rub issues

wheels
F 21x9 et30
R 21x10.5 et35

tires
F 255/35/21
R 295/30/21