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Does tire size affect gas mileage?

Posted: Wednesday, October 13th 2010

Fuel efficient tiresTires can play an important role in making cars more fuel efficient.  Many motorists are familiar with the concept of maintaining proper tire pressure to attain optimal gas mileage.  Tires that are overinflated or underinflated will not be able to maintain proper rolling resistance, which will reduce the vehicle’s gas mileage.  In addition to tire pressure, many motorists wonder whether tire size is also a factor.

The impact tire size can have on performance, including fuel efficiency, was examined in a recent issue of Car and Driver magazine.  The article, titled Plus-Size Models: Testing the performance effects of upsizing wheels and tires, was written by Tony Quiroga and appeared in the April 2010 edition.  The findings in the article were based on tests involving “nearly identical Goodyear Eagle GT ultra-high-performance all-season tires in all five sizes, inflated to manufacturer-recommended pressures.”  In addition, they “used the stock steel wheels for the 15-inch test and went to the aftermarket for the larger wheels, as most owners would do. The aftermarket wheel … was a cast-aluminum ASA GT1, which is available in 16- to 19-inch sizes on the Golf.”  One sentence offers a succinct summary: “What’s immediately apparent from the results is that as the wheel-and-tire packages get larger and heavier, acceleration and fuel economy suffer.”  Specifically, the author cited a “10-percent drop in fuel economy … from the 15s to the 19s.”

The question of whether tire size affects gas mileage is not a new one and it is not limited to cars or personal vehicles.  It was examined in an article in the December 2000 issue of Land Line Magazine, which is described as a business magazine for professional truck drivers.  The article examined the issue of how tire specifications can affect fuel economy.  Paul Abelson, the magazine’s technical editor, interviewed Peggy Fisher and Asa Sharp, both considered experts in this field.  They addressed the issue of how “tire size and profile affect fuel economy.”  They explained, “When low profile tires first came out, they were about 4 percent more fuel efficient. Low profile sidewalls are shorter, and therefore stiffer. That reduces flex but only slightly. Smaller tires weigh less than larger tires, so less energy is needed to get them rolling, and also to stop them.”

The experts, however, offered a word of caution lest truck drivers assume they should switch to smaller tires:

It is probably not worth switching to smaller tires, since any gains in fuel economy would be offset by the added cost of re-gearing to keep your engine operating in its most efficient rpm range. Remember, power and economy are affected by transmission, drive axle ratios and tire size (revolution per mile). Change one, and you throw the equation off. With today’s new tires, there is virtually no difference in mpg due to tire size.

As with many questions related to cars and tires, the answer to this question can have nuances, conditions, and variations.  The answer that applies to truck drivers is different from the answer for the typical motorist.  Before purchasing new tires, consider whether some of the aforementioned factors, such as your vehicle’s transmission, would be impacted positively or negatively by new tires, particularly if they are of a very different size.  Tire treads can also affect your fuel efficiency, but depending on the conditions you drive in, safety should be a priority.  There are many factors to consider when buying tires… let the experts at Dunn Tire help answer your questions.