In an SAE discussion group I recently came across a discussion about tyre pressures and fuel economy. Here is a reply to the question: “Has anyone done a comprehensive study on how exactly tyre pressure effects gas mileage?” A colleague in the forum replied as follows:
“Yes, I have.
for the past thirty years I have kept tire pressure set at 42 psi in my cars. There has been no significant change in the tire ‘footprint’, no effect on real world anti-lock braking, and an appreciable increase of 4-5 mpg, and increased tire life.
Back in the ’70’s, I taught an advanced diagnosis R/D course at a NJ college. Students were ready to graduate at the end of the course semester. The training facility had an in ground chassis dynamometer. Students were divided in small groups of three and were instructed to do anything they wanted to reduce road horsepower, ie.increase mpg, required to keep the vehicle rolling at a constant speed/load.
Students reduced vehicle weight, (by removing components such as seat, weighing them, then subtracting the weight via the dyno control panel), changed aerodynamics by figuring wind drag based upon frontal area and known factors, engine modification to include such things as five angle valve refacing, camshaft profile changes, etc., elimination of catalytic converters, and tire pressure. Proper research procedures were followed to ensure as accurate as possible results. Having taught this course several times with different students, vehicles, etc., there was only one vehicle change that effectively changed fuel economy, tire pressure.
Students increased tire pressure from the then specified 28-32 psi specification, a little at a time until a measureable change was found. Research was done regarding the development of the radial tire. Use of the radial tire in performance racing applications. Also research on the bias ply/radial tire, today known as emergency vehicle tires.
Vehicle mpg increased, (road hp required decreased), as the tire pressure was increased up to approximately 45 psi. Beyond that, there was no appreciable mpg increase.
Tire manufacturers informed the students that the sidewalls of a radial, being flexible, straighten out with increased tire pressure, leaving the ‘footprint’, unaffected. Also, that radial tires were originally produced and operated at 60 psi, (back in the early years, ’50’s). This was how students decided to experiment with tire pressure.
So, as a result, the tires of my cars are inflated to 42 psi and my truck tires to 55 psi. I have enjoyed the maximum mpg and tire life. Claims of poor tire life from factory tires have been negated.
[…] Hope you found this helpful. Just don’t plagiarize. Thanks” (Source: Fred Allen, retired automotive professor, 43 years , Rockport ME, USA)
What do you think about this? Fred’s experience is clear but are there any potential problems with increasing tyre pressures in this way? All sensible comments welcome!