The Writing Is On The (Side) Wall

Greg Zyla
Q: Greg, if I inflate my tires past the recommended tire pressure number by a few pounds, will I get better gas mileage in both my muscle car (1970 Plymouth Barracuda) and my street car 2010 Dodge Avenger R/T? My friends say it is OK, but I don't feel I should go past the recommended tire pressure.
Also, will the car handle better in the turns if I under inflate by a pound or two? Allison, email from Texas.

A: Allison, your friends are correct, theoretically, in that more tire pressure will help gas mileage and also increase top speed, but doing so is not good advice.
First, even though a few more pounds of air might increase mileage just a bit, the ride would become more pronounced and rough, and handling in turns would be reduced because the tire is "pumped up" too much, losing needed suppleness and adhesion.
However, don't feel that if you lower your pressure under manufacturer recommendations, you'll have a better handling car. My friends at several major tire companies all agree that tires under-inflated by 6 psi (pounds per square inch) increases tire rolling resistance by 10-percent or more reduce fuel mileage and increase tread wear rates and tire fatigue. I also want to add that under inflated tires raise temperatures inside the tire,which is not good.
We all recommend the following in maintaining a proper inflation level and in checking tire wear (a vehicle's proper inflation level can be found either on the door jam, on a placard in the glove box or, better yet, on the tire itself:
  • Check tire inflation pressure (including the spare) at least once a month and before every long trip. Tires must be checked when they are cold; that is, before they've been run a mile. Also remember in the dead of winter, tires loose air pressure naturally the colder it gets, usually one pound per 10-degree drop in air temperature.
  • If under-inflated, inflate the tire(s) to manufacturer recommendation.
  • Tires should be rotated at least as stated in the owner's manual every 3,000-8,000 miles and the alignment should be checked once a year. I personally rotate every 4,500 miles.
  • At least once a month, the car owner should inspect the tires closely for signs of uneven wear. Improper inflation pressures, misalignment, improper balance or suspension neglect may cause uneven wear patterns. If not corrected, further tire damage will occur.
  • Finally, it doesn’t matter if your car is a collector car or daily driver…use correct tire pressure at all times.
 Thanks for the question.
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