In a 6x2, only one of the tandem axles is a "live" drive axle. In a column last year, Senior Editor Tom Berg wrote that one drive axle carrying enough weight will push the truck or tractor over pavement better than two of them, because each axle of a "live" tandem will have less weight and less traction.
Fewer gear sets also means hundreds of pounds of weight savings and also reduces parasitic friction for better fuel economy.
Last year at MATS, Meritor showed off a concept tandem for a 6x2 axle configuration, with differential lock and weight adjustment functions done automatically, when the integral ABS and traction control sense wheel slip in the drive axle.
This year there was even more to see and hear about 6x2s.
Two of HDT's 2012 Truck Fleet Innovators have been testing 6x2s to save weight and improve fuel economy, and shared their thoughts as part of a panel discussion during the 2012 MATS Fleet Forum, the day before the show.
Phil Braker, vice president of operations, Nussbaum Transportation, says new truck specs featuring a 6x2 have been so successful that the majority of the fleet's linehaul tractors will be 6x2s going forward. One thing that's a must, he said, is an electronically controlled air suspension, so the truck will automatically adjust air to the drive axle as it finds slippage.
While resale value was something they thought about in making a decision, Braker said, "we're building the truck for today; we know it works from a fuel economy standpoint. If more larger fleets will embrace the technology and use it, it's going to be more common out there. There will be people who will say, 'I'd gladly buy a used truck with that technology if it gets 8 mpg.' Fuel savings have been more than enough to pay for a few tow bills if drivers get into trouble in some soft gravel."
Mike Jeffress, vice president of maintenance at Maverick Transportation, has been testing a few 6x2s as well. "My comments are very similar to Phil's," he said. "The traction issues we've had, the technology isn't completely developed yet, we're helping the industry work through the problems and get that system to where it is more acceptable through the nation. On the residual side, we do feel the bigger fleets are going to get on board."
Both say they're seeing about 2/10 mpg improvement in fuel efficiency with the 6x2s, although Jeffress said his primary purpose is to get back some of the weight lost to emissions aftertreatment systems.
Meritor this year announced its new FueLite 6x2 tandem axle, the first member of its SoloDrive Series axles which features 6x2 tandem rear axles.
Based on the Meritor 160 series drive axle, the FueLite tandem axle offers nearly 400 pounds in weight savings and approximately a 2% increase in fuel efficiency when compared to a traditional 6x4 configuration, according to the company. All SoloDrive Series axles use the same rear-tag axle for simplified maintenance and are designed to work best with Meritor brakes and options. Watch for a second addition to the line later this year that will address traction concerns.
Bendix Commercial Vehicle Systems said later this year it will introduce Bendix eTrac to automate air pressure transfer on 6x2 tractors and trucks, addressing potential concerns about traction.
This will address a trend of more fleet interest in spec'ing 6x2 configurations, where only one axle of the tandem is a live drive axle, for several hundred pounds of weight savings as well as fuel economy improvements, explained T.J. Thomas, Bendix director of marketing and customer solutions, Controls group.