Recommended tire pressure PSI versus MPH

[packardv8]

My wife's XWD 3.0 has the 18" tires and a recommended pressure of 35 PSI. When we picked up the car at Ken Garff's in Salt Lake City, it had 34 PSI and got 21.5 MPG on the first road trip back to Spokane.

This time, same stretch of I-84 through Idaho and Utah, but loaded heavier, I increased the tire pressure to 39 PSI. At a cruise-controlled 78 MPH, the mileage was 24. This included climbing several 5500' mountain grades at 4200 RPMs.

The higher pressure does not noticeably detract from the highway ride. On Spokane's bomb-cratered streets, I'll go back to 35 PSI.

jack vines

[Dave T]

Recommended tire pressure is not gospel. Mercedes Benz summed it up nicely. In their owner's manual, they said to use 3 psi more pressure than the tire pressure on the door sticker for better gas mileage and better handling at the expense of worse ride. In other words, they said you could choose. That is the only car company that is so frank with the subject.

Since I now have a number, I apply that to my Saab. I put 3 psi more than on the door sticker. In fact, in the winter when it is cold and wet, I put 4 psi more. That usually means that I don't have to put air in the winter tires because they are on only about 3 months and might lose 2-3 psi during this time.

[nordwulf]

Was it the same stretch of highway in the same direction? I think new engines generally have higher fuel consumption in the beginning but perhaps that's just a myth.

[packardv8]

Yes, same stretch of highway in the same direction. The car was a demo and had about 3,000 miles on it when we bought it.

jack vines

[kurwa311]

I use 38 PSI since it is told in the book to have such pressure if you drive faster thatn 160km/h............ But stock tires is pure shit. change it as soon as poosible to something with Y or at least W rating.