Folks: I will be getting new tires soon and probably will be going with Michelin Pilot Sport 4S. I am torn between the 2 sizes below so you gurus let me know if either of these sizes will fit on my SL (OEM Front: 225-45-18, Rear 255-35-20) without having any ABS, traction, etc, ( nanny issues).
1. Front: 235-50-18 Rear 255-40-20
2. Front: 245-45-18 Rear: 255-40-20
If both will fit, which would you recommend and why? Thx guys.
Based on a quick look at Discount Tire's Tire Size Calculator (Tire Size Calculator | Check Tire Size Conversion | Discount Tire), I'd expect problems using either set. Generally, changes over about 3% or so will trigger problems with the nannny controls. Your rear tire choice is 7.7% larger than the stock size. Your front tire 235/50-18 would be 4.9% larger and the 245/45-18 is closer to acceptable at 2.7% larger than stock. When changing front and rear sizes, try to change both by the same amount or as close as you can. Since the speedometer/odometer are driven off the rear wheel, the 255/40-20 will actually be turning at 70 mph when the speedo shows 65.
http://www.willtheyfit.com will also let you see how different wheel/tire sizes will fit/look.
Here's a pic of the differences -