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There is a question at the end of this, so please bear with me.
My S60 (manual transmission, non-turbo, 195/65-15 tires) has, listed inside the fuel filler, the following tire pressure recommendations: "38 psi fuel economy; optional pressure 32psi front, 30psi rear." I've generally used the optional pressure, but with warmer weather the tire pressures have gone up a bit with the cooperation of some basic laws of nature. So I let nature run its course and even added a some air, getting pressure up to about 35psi when cold.
The result: Fuel economy increased dramatically over my usual 30-31mpg. On a recent trip to northern New England (lots of cruise control at 67mph, few if any stops, and nearly ideal weather) I averaged 34mpg. When my tire dealer switched me back to summer tires, they put 38psi in each when cold, and I again let nature run its course. (I asked them about the 38psi, and they said it was according to specs.) The result was an even better 35 miles per gallon in highway driving. This is about what my wife-to-be gets in her Toyota Corolla -- on a good day.
Downside: A jittery ride and some squeaks and rattles in the dash that I never heard before. I haven't noticed much change in road grip while cornering, but then my days of "enthusiastic" driving were over long ago.
Anybody else using 38psi air pressure? Will this impair my braking distance or emergency handling? I'm comforted that Volvo, Nokian, and my tire dealer are unanimous in recommending the higher pressure, but this is more than I've ever used before in this or any other car. And, yes, it's well below the "maximum" listed on the sidewalls of either my Nokians or Michelins.
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