Maximizing fuel efficiency is a goal for many drivers. After all, what you save at the pump, can be invested, saved, or used for a splurge. Many drivers know that flat or underinflated tires decrease fuel efficiency. Under inflated tires also negatively affect maneuverability.

So if under inflated tires decrease fuel efficiency, do over inflated tires increase fuel efficiency?

In 2009, Popular Mechanics reported that its staffers put the theory to the test. (PLEASE DO NOT TRY THIS ON YOUR OWN!) They chose a 400 mile route. The vehicle they chose recommended 32 pounds per square inch (psi) in each tire. The sidewall of the tires indicated a maximum of 50 psi. They inflated the tires to 45 psi for leg one of the test to compare. On the return trip, they decreased the tire pressure in all four tires to the recommended 32 psi.

The first leg of the trip used 9.34 gallons or 35.36 litres of fuel, which translated to 42.19 miles per gallon (mpg) or 17.93 kilometres per litre (kpl).  The second leg of the trip used 9.76 gallons or 36.95 l of fuel, an increase of .42 gallons or 1.59 l, or 42.14 mpg or 17.91 kpl.

They concluded that over inflating the tires didn’t offer significant enough fuel savings to overlook the decreased handling and ride quality.

Author Ben Stewart reported, “At 45 psi, the ride was brittle. In fact, the tires were so stiff they nearly vibrated our garage door opener right off the sun visor. Ouch.”

So, over inflated tires do not increase fuel efficiency significantly enough to warrant pumping up; please, don’t try it. The extra pressure increases the likelihood that the tire will fail by sudden impact.

How inflation affects tire health

Improperly inflated tires not only affect handling and drive, but they also affect the health of your tire.

Under inflated tires increase rolling resistance. In some circumstances, the added grip is welcome, but if you continue to drive on underinflated tires the edges of the tires will wear down more quickly. Under inflation can lead to excessive heat built up that could result in internal damage to the tire. Additionally, the lower air pressure will decrease the load capacity, or how much your vehicle can carry. Lastly, lower air pressure will increase the amount of give or flex in the sidewall and can lead to tire failure.

Conversely, an over inflated tire will have lower rolling resistance, but the increased air pressure will cause the tire to be overly rounded and lead to the center of the tread wearing down more quickly than the edges of the tread. Maneuverability will be compromised. Additionally, you’ll experience a harsher ride and feel like you’re bouncing, rather than rolling, down the road. Lastly, the extra pressure in the tire increases the odds the tire will fail upon impact.

Whether your tires or under inflated or over inflated, they will wear unevenly and cause you to replace them sooner. Additionally, improperly inflated tires decrease safety for you, your passengers, and your fellow motorists without offering much in the way of increased fuel economy.

What you can do to improve fuel efficiency

  1. Here are some things you can do to improve your vehicle’s fuel efficiency safely:
  2. Keep your tires inflated to the recommended pressure and check them periodically. Your local Go Tire professional can help you determine the proper levels for your tires and vehicle.
  3. Allow your engine to warm up a bit by driving gently. Idling to warm up uses more fuel than driving does.
  4. Slow down. Most cars’ fuel efficiency peaks between 35-60 mph or 56.3 -96.6 kph. Above 60 mph or 96.6 kph, fuel efficiency drops significantly. The U.S. Department of Energy reports that every 5 mph or 8 kph you drive above 60 mph or 96.6 kph, your fuel efficiency drops by 7%.
  5. Avoid idling.
  6. Keep your vehicle in shape with regularly scheduled maintenance.
  7. Use the recommended grade of motor oil.
  8. Use cruise control on the highway to maintain a constant speed and save gas.
  9. Keep your tires aligned and balanced.
  10. Decrease the weight in your vehicle. Avoid carrying unnecessary items. An extra 100 pounds or 45.4 kg can decrease fuel economy by up to 2%.
  11. Remove your roof rack to reduce drag. A loaded roof rack can decrease your fuel economy by as much as 5%.

Additional Source: http://www.cartalk.com/content/guide-better-fuel-economy