Well courtesy of GM, I have conducted a simple experiment on of the effect of tire pressures on gas mileage, at least for one vehicle and one set of tires. My Vue, when delivered, had a recommended tire pressure of 30 mpg all around (which I maintained). After the vehicle flunked the NHTSA extreme maneuver rollover test, GM revised the rear suspension and upped the recommended tire pressure to 35 psi. For the 7000 miles before the change, the car averaged 22.1 mph. For the 7000 miles after the recall (and the change to 35 psi), the mileage was 22.9 mpg. I was surprised at the difference. In fact, before the tire pressures were revised I never had a
7000 mile segment where the average fuel mileage was over 22.4 mpg. (low for a 7000 mile segement was 20.9, high 22.4) So, it seems to me that inflating the tires an extra 5 psi increased the fuel economy by 0.3 mpg to 0.8 mpg. I would have thought if this was typical, GM would have specified this pressure from the beginning. On the other hand, the car is now much more nervous when driving. It reacts to subtle changes in the road, and reacts quickly to minor steering inputs. The ride is not much different, and in fact, after a few months, I can't tell any difference in the ride quality. I just replaced the original Bridgestone tires with Michelin LX4's, so it will be interesting to see what happens to the fuel mileage now. Of course the difference in fuel mileage might be related to other changes, but I don't think I made any significant changes in my driving pattern recently, especially since the variance between other 7000 mile segamens was around +/- 0.25 mpg (21.15 +/- 0.25 mpg).Regards,
Ed White