Fleet Management News & Business Info | Commercial Carrier Journal
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28 COMMERCIAL CARRIER JOURNAL | NOVEMBER 2014 in focus: TANDEM AXLES F or a long time, 6x4 drive axles on heavy-duty commercial vehicles were the default spec for fleets regardless of application. The thinking was straightforward: Torque was king, and getting a load rolling as quickly as possible was a primary con- cern. Diesel fuel wasn't as expensive, and there was little reason to consider any alternative axle options. Today, fuel economy is a vital interest for fleets with razor-thin margins and competitors breathing down their necks. To help alleviate those worries, more fleets are turning to 6x2 tandem axles, which have made significant in- roads for a variety of reasons, including higher-horsepower engines and more efficient drivetrains. According to a recent study by the North American Council for Freight Efficiency, a 6x2 tandem axle will provide an average 2.5 percent im- provement in fuel economy. As with many new technologies, however, several disadvantages offset the benefits derived from running 6x2 tandems as a fuel-saving spec. "The benefits are both fuel economy and weight reduction," says Brad Wil- liamson, marketing communications manager for Detroit. In many applica- tions, 6x2s are available with faster axle ratios, which deliver even greater fuel economy, Williamson says. In terms of how they work with a truck's powertrain, 6x2 axles aren't much different from a standard 6x4 configuration; the engine and trans- mission still deliver power to the driveline and then to the axle and tires. Williamson says a 6x2 axle's main benefit is the reduction of mov- ing and interacting parts, creating less friction loss and therefore reducing rolling resistance. "Reducing the rolling resistance improves fuel economy by allowing the energy created by the powertrain to transfer to the ground with fewer losses so that there is more usable power to move the vehicle," he says. Dave McCleave, director of market- ing for Hendrickson, acknowledges that removing a drive tandem axle reduces weight and results in a 3 percent fuel economy improvement due to the elimination of parasitic losses. "How- ever, the 6x2 application is limited by traction concerns, particularly when bobtailing or partially loaded," McCleave says. To address these limitations, Hen- drickson designed its Optimaax liftable forward tandem axle to lift the forward axle automatically when loads are light and to shift the unsprung weight to the rear drive axle without overloading it to provide additional traction and enable 6x2 applications. "Additionally, an empty or lightly loaded tractor has the ability to operate as a 4x2," McCleave says. This config- uration eliminates the forward drive axle's rolling resistance, as well as thrust and tandem scrub, allowing fleets to adjust their axle settings to meet the application at hand, he says. In the lifted position, a minimum 2 percent fuel economy improvement is gained, resulting in more than a 5 percent improvement compared to 6x4 configurations, McCleave says. "When rolling resistance, thrust and tandem scrub is removed by having the forward tandem axle in the lifted position when the capacity is not re- quired, powertrain components are not working as hard," he says. "This plays a part in the overall fuel efficiency gains for the vehicle." Optimaax's flexibility is suited for bulk and other variable-load haulers, including large deadhead runs, McCleave says. There is more usable power to move the vehicle. – Brad Williamson, marketing communications manager, Detroit New 6x2 options boost fuel economy, flexibility BY JACK ROBERTS When only one is needed Hendrickson's Optimaax is de- signed to lift the forward tandem axle automatically when loads are light and shift the unsprung weight to the rear drive axle without overloading it.