It’s still an oddball spec in road tractors and you’re not likely to consider it, but the 6x2 – a single drive axle with two powered wheels among six total wheel positions – will someday become more common as truck operators look for ways to save fuel and cut tare weight, suppliers think. Today, progressive fleets are testing or embracing it, and it might even be a good choice for some owner-operators.
The 6x2 has an interesting history. When the Swedes from AB Volvo came to America in 1981 and ’82 to help resurrect the products of the bankrupt White Motor Corp., they were astonished to see road tractors running up and down our highways with “live” tandems. As now, these split engine power among four wheel ends of two driving axles, and along with the non-powered steer axle, the chassis was called a 6x4. This was a complicated and heavy way to do the job, the newcomers thought.
“Why do Americans use the 6x4?” one of the Swedes asked incredulously during a reception at Volvo Trucks’ headquarters in Greensboro, N.C.
“To get better traction,” I recall answering.
“You don’t need it,” he insisted. The 6x2 tandem with a liftable dead axle worked as well, weighed less and cost less money, he said. That type of 6x2 was common on the highways of Europe. It still is, even on trucks that trundle over muddy trails into the woods to pick up timber.
A couple of years later, Volvo flew a group of truck writers to Sweden to show us their European products and explain how some of those designs were starting to transfer to their American-made trucks. At one point a couple of the engineers who had expressed frustration with our 6x4s demonstrated how a 6x2 truck could plow deep snow. They let us drive it on a frozen lake to see and feel for ourselves how it performed.
The truck, a municipally owned Volvo N10 dumper outfitted with a large V-plow in front and a wing plow on its right side, moved the snow easily, because its dead tag axle was raised and its chained drive tires carried about 22,000 pounds, giving it considerable traction. The wing plow sometimes kicked the rear end a bit to the left, but then the truck would recover and all the while we continued to move.
That experience caused me to write a column in HDT describing the 6x2, and at least one guy – an owner-operator from Indiana named Fred Butchers – read it and was inspired enough to buy a new road tractor with the arrangement. It was an ’84 Kenworth K100 Aerodyne cabover with a pusher-type dead axle ahead of its drive axle. Otherwise it was Euro-style, with a driver-controlled dump valve that drained air from the rubber bags over the pusher and lifted it off the ground. That transferred weight to the drive axle and gave him all the traction he needed.
Because Fred kept careful records, he knew it saved him money in fuel. And, he told me during a visit a few years after the purchase, he also saved toll money on turnpikes because while lightly loaded he could keep the dead axle raised, and was charged the four-axle combination rate instead of five. We kept in touch over the years, and he eventually reported that he had run the KW for 1.2 million miles, and was always glad it was a 6x2.
Formal tests of 6x2 tractors show fuel economy gains of 2% to 3% over 6x4s, but some fleets report as much as 5% better fuel economy due to less parasitic loss from fewer gear sets. And a 6x2 weighs 350 to 450 pounds less. A downside is higher tread wear on the drive axle’s tires. Those should be beefier, and tires on the dead axle can be rib types, even trailer tires, the experts say.
Most truck makers now offer 6x2 options, and it’s still possible to order a manual system like Fred’s. But modern systems from Meritor and Dana Spicer feature automatic weight-transferring functions and auto-locking of the drive axle’s differential. Demonstrations show that with extra weight on the drive axle, traction is very good. One of the Dana systems is “convertible” in that it can be retrofitted onto an existing 6x4 tractor and turned back into a 6x4 at trade-in time, which handles the problem of lower resale value.
The Truck Blue Book says a late-model 6x2 tractor is worth about $11,000 less than a 6x4, and for 2007-09 models it’s worth $5,500 less in residual value. But 2004-06 tractors are worth $700 more with a 6x2. Go figure.
So, is a 6x2 for you? Maybe, if you keep careful records, closely watch maintenance and drive intelligently. Certainly not if you run a dump truck or something else that goes off road a lot. Probably not if you run on pavement but would rather stick with the tried-and-true that won’t be hard to sell. Then again, suppliers think the 6x2’s popularity will increase from the current 3% of all Class 8 sales to as much as 18% in five years. So it might not be such an oddball spec after all.
Related Story: Test Drive -- Meritor's 6x2 SmarTandem
Read more about 6x2s in the May issue of HDT.