Under Pressure to Achieve Fuel Efficiency
By Todd Kaho
 Experience really is the best teacher. I’ve been thinking about fuel economy a lot lately and perfecting the art of driving as efficiently as possible has become an obsession. Long a performance junkie, the achievement of extracting a bit more speed out of the vehicle, turning a quicker lap time, or simply driving the perfect line through a corner is all too familiar. Extracting great mileage from a vehicle is the same...it’s just a different measure of performance. Topping off and proving that you beat the official EPA numbers on that tank is a good feeling.
Our long-term Mercury Mariner Hybrid test vehicle has been a great instructor during my quest for efficient driving skills. The onboard navigation system offers a fuel computer that graphically illustrates instant and average fuel economy for the previous 15 minutes of driving. Understanding how the hybrid system works and fine tuning driving style using the fuel computer’s information allows me to regularly beat the Mariner’s EPA economy numbers. There are times when that’s not possible due to the mission at hand, but overall, the Mariner and I are in sync when it comes to squeezing every drop out of every gallon.
So when the Mariner’s mileage suddenly dropped by 2-3 mpg a few months ago, I was quite intrigued by what made the difference. Colder temperatures on late fall mornings were my first thought, but I wasn’t ready to jump to conclusions. Then one particularly cold morning, with the mercury (both the Mariner and the temperature) hovering around 20°F, the following message appeared on the Mariner’s information center: “Low Tire Pressure.” Mystery solved. The cold temperatures were partially to blame, but weren’t the whole story. A quick check with a digital tire pressure gauge showed the tires were indeed more than five psi below the recommended pressure, partially caused by the colder temperatures, but mostly by my complacency in checking them as often as I should.
The first major routine maintenance on the Mariner isn’t scheduled until 10,000 miles and includes the first oil change. The temptation is to just put gas in the tank and point the Mariner where you need to go. But every few fill ups should include a tire pressure check if you want to maintain peak performance and economy. I know that, but this experience underscored the importance of keeping the tires properly inflated.
Tires are the critical link, a vehicle’s only connection (hopefully) to terra firma. One of the many pearls of wisdom garnered at this year’s Michelin Challenge Bibendum was the fact that tires consume 20 percent of the energy necessary to move a vehicle down the road. You read that correctly: one fifth of the power your vehicle produces is soaked up where the rubber meets the road. Rolling resistance is a huge component in modern tire design that relates directly to fuel consumption. Consider that a 50 percent decrease in rolling resistance would lead to a 10 percent increase in fuel economy. That’s a quantum leap in fuel efficiency. Over the past 10 years, Michelin has reduced rolling resistance by 30 percent in passenger car tires. As you might imagine, there is a delicate balance to be maintained when engineering a tire. Measures that reduce rolling resistance often have a negative effect on safety related parameters including cornering and braking grip, and water evacuation under the tire to minimize hydroplaning. Obviously, building greener tires is a science well worth pursuing.
With our long-term Mariner Hybrid tires properly inflated, fuel economy bounced back to meet or exceed EPA estimates. It’s amazing what you can learn – or relearn – when you pay attention to the details.
|
