Just bought a 09 Taurus X. It came with 17" wheels and tires. I see there was a 18" option. Would it be to my advantage to upgrade to the bigger wheels and tires when it is time to replace the tires? Since retirement and the price of fuel has become unstable, we decided to down size our daily driver. Thanks for any input. Bert

 

I don't really see where it would gain you anything. The PCM and other moduls would need reprogrammed to compensate for the larger wheels.

 

Basically the stock 17" (215/65-17) and the optional 18" (225/60-18) tires are the same size in diameter (18" is 1/4" taller) netting the same amount of engine RPMs. The only gain going to an 18" tire is a different looking rim and a more expensive tire. A taller side wall'd tire will always ride better. That's why I went from a 235/60-16 to a 235/70-16 tire. In my case, the 235/70-16 tire is 2" taller resulting in a lower RPM at highway speeds. You're only talking about 200 RPMs and about 50 less revolutions of the tires per mile.