Fleet Management News & Business Info | Commercial Carrier Journal
Issue link: http://read.dmtmag.com/i/599511
commercial carrier journal | november 2015 67 EquipmEnt: 6x2 AxLES penetration was 2.5 percent," Roeth says. "Our prediction was that we thought that number would double every year for the next four to five years and level off somewhat." But based on the industry response at TMC, Roeth thinks a concurrent commercial vehicle fuel economy report from the U.S. Environmental Protection Agency might provide an even more accurate take rate. EPA projected that 60 percent of Class 8 tractors engaged in long-haul applications would be using the 6x2 axle spec by 2024. "The EPA doesn't buy trucks, but they are pretty detailed in the studies they put out," he says. "I think there's some indi- cation that this will become something of the industry standard for long-haul- spec'd trucks in the next few years." Application, driver buy-in The 6x2 drive axle concept is fairly straightforward and widely accepted outside of North America. In Europe, they are considered the standard spec for long-haul tractors. North American fleets today can spec two variations of the 6x2 axle system from suppliers such as Dana and Meri- tor. Both versions feature an unpowered "dead" axle that normally would be powered in a conventional 6x4 drive axle package. The main difference in the two 6x2 specs centers on which axle is powered and which is "dead." The more com- mon system, according to NACFE, is the "tag tandem" configuration, where the forward-position rear axle is driven and the second-position axle is not. Alter- nately, the "pusher tag" 6x2 features the rearmost being powered with a "dead" or tag front-position axle. Both versions are offered with 40,000- and 46,000-pound ratings, as on 6x4 axles. Both also feature tag axles specifi- cally designed to carry the same load as the powered axle. The fuel economy and weight-saving benefits from 6x2 axles come from the fact that an entire set of inter-axle drive- shafts and gear sets have been removed from the vehicle. This lack of internal gearing cuts parasitic fuel loss from internal friction and lubricant churning. "It also cuts about 400 pounds off over- all vehicle weight, which further con- tributes to both vehicle freight efficiency and higher fuel economy," Roeth says. To compensate for the higher power and torque loads being transmitted to a single drive axle, 6x2 inter-axle compo- nents are slightly larger and more robust than those found on 6x4 units, coupled with a 23,000-pound maximum haul weight per axle when compared to a 20,000-pound haul weight on 6x4 axles. "With a 6x2, you get lower weight, re- duced maintenance effort and costs and higher fuel economy," Roeth says. "It's a pretty attractive combination for fleets, provided they are in the correct applica- tion to run this spec." Ryder System was one of NACFE's partners on its 6x2 test program, and the truck rental and leasing company was interested in the concept's performance and usability at an early stage. "Delivering the best possible fuel economy for our customers is always top of mind for us," says Scott Perry, Ryder's vice president of supply management and global fuel products. "In the right applications, a 6x2 drive axle absolutely delivers substantial fuel economy ben- efits, but it is important to understand that this is not an ideal spec for every truck fleet out on the road today." Managing the negatives Despite its many benefits, the 6x2 con- cept has a distinct traction disadvantage, Perry says. "You really have to look hard at duty cycles if you're a fleet manager considering this spec," he says. "If you're in coast-to-coast or even regional-haul applications, this may work for you, pro- vided you're hauling below the Mason- Dixon Line or in climates with limited inclement weather. Good roads with a lack of uneven surfaces are another plus factor." The axles are not a good fit in regional haul or pickup-and-delivery applica- In collaboration with the Carbon War Room initiative, the North American Council for Freight Efficiency studied existing literature on, as well as new track tests of, 6×2 tractor axle configurations and fuel efficiency versus that achieved with more common 6×4 setups. Tests examined and performed showed a range of increased efficiency from as little as 1.6 percent to as much as 4.6 percent. NACFE concluded an average 2.5 percent could be expected for many fleets with a conversion to a 6×2 configuration. This will become something of the industry standard for long-haul- spec'd trucks in the next few years. – Mike Roeth, NACFE executive director