For a while, I was running tire pressures in the high 40s, to get the best MPG. But the ride had been too harsh on the 17" Toyo tires. On some bumpy back roads at night, I felt like the headlights were going to get shook off the car, from watching the LED beam cut off shaking to the bumps. All the interior rattling was getting annoying too. So I gave up. I settled on 39F/38R. Seems to be comfortable, and quiet. I might experiment with higher pressures when I get new, and different tires, but for the time being, +6 PSI is all I am good for.
Our OEM's are 215/45R17. I settled on 38/36 (front/rear), with the low profiles. I do set our winter 195/65R15's a fair bit higher.
I go with recommended pressures. Better for the tires, much safer, better ride. Car is rated for 50 mpg with the recommended pressures. I put the "riding on rocks" up there with using lap blankets and gloves vs. the heat or sticking the head out the window vs. turning on the AC when it's 100...a mpg too far.
The mpg gain from increased tire pressure is largest for the first few extra psi. After that the effect provides diminishing returns and the cons start stacking up. I find that between 38psi and 46psi provides the most gains while reducing the negatives. Obviously the exact number will depend on the driver's comfort level, the surfaces they drive on, the outside temps/weather, the speed the regularly drive, the exact tires used, etc..
