Going low

By James Jaillet | December 01, 2010

Goodyear’s Tim Miller says retrofitting can be done, however, by modifying the gear ratio to ensure the engine is running at maximum efficiency. Other changes, like calibrating the odometer and the speedometer to match the new tire sizes, would need to be done as well.

ON/OFF-HIGHWAY. Walenga says low-pro isn’t a good fit for on/off-highway applications because the shorter sidewall, due to its stiffness, doesn’t deflect as much as a tire with a taller sidewall. It’s not built to take the beating of off-road use.

URBAN. Miller says low-pro tires should be avoided in any application in which damage to the sidewall or the wheel is likely to occur. “You’re putting your vehicle closer to the ground and closer to the curb. Going with low-profile would do more harm than good in those situations.”

Wide-base singles

The new generation wide-base tire amplifies some of the benefits seen by low-profile duals, says Goodyear’s Tim Miller.

The Heavy Drive Long-Haul Deep Lug tire from Continental has a 32⁄32-in. tread depth and the Eco Plus’ compounding offers a lower rolling resistance. Its wider tread offers better wear.

“Replacing two tires with one lowers overall vehicle weight, which helps fuel economy. There are only two sidewalls instead of four, which makes them more efficient and helps them run cooler. Rolling resistance is also reduced, which allows an operator to spend a little less on fuel every month.”

Wide singles have an aspect ratio around 50 percent, due to the short sidewall and the extra width. However, because the sidewall height can be the same as that of other low-pro tires, they can be direct replacements for low-profile duals since their height won’t change the gearing of the truck. They are not replacements for tires with standard sidewall height.

Bridgestone’s Guy Walenga says fuel savings aren’t an inherent guarantee when switching from duals to a wide single because tires have so many attributes. “Tires can be engineered for fuel efficiency,” he says. “There are different tires, different manufacturers, different tread depths, different compounds – you have to take all of that into consideration.”

Low-pros by definition

A sidewall with a shorter height than width is deemed low-profile. These two measurements also yield the aspect ratio – the sidewall height measured in a percentage relative to the width of the sidewall at its widest point.

The aspect ratio of 11R22.5 tires – the typical height of the standard tire – is about 100 percent, meaning the sidewall height and width are the same, says Don Baldwin, product category manager at Michelin.

Low-pro tires’ aspect ratio is around 80 percent, Baldwin says, though some are lower.

These measurements are what constitute the tire’s sizing nomenclature. For instance, a low-profile 295/75R22.5 is 295mm wide at the tire’s widest point. It is 75 percent as high as it is wide – 75 percent of 295 mm, says Guy Walenga, director of engineering for commercial products at Bridgestone.

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