“Today’s emission-controlled engines are heavier. I will need the weight savings of a 6x2 to offset some of that increased weight.”
Fleets switching their tractors to 6x2 axle configurations could realize a 2.5% fuel reduction, among other benefits. Since the original Confidence Report on 6x2 axles issued in January 2003 , 6x2 adoption among North America long-haul fleet has increased from approximately 2% to 4–5% in 2016. However, many fleets still view them as a niche offering suited for the southern region of the U.S.
Factors that have contributed to the limited adoption of 6x2 axles include: low fuel prices, higher tire wear, driver perception, residual value, and improved efficiency of 6x4 axles.
However there is reason for optimism with 6x2 technology. Through a combination of best practices and adoption of complementary technologies, fleets have found that 6x2 axles work for their application and are benefitting from the improved fuel consumption.
One promising new development is 6x2 tandem axles with liftable pusher axles. Click here for more information on liftable 6x2s.
6x2 axles offer a 2.5% reduction in fuel use, with our study participants enjoying fuel economy improvements from 1.6% to 4.6%
6x2 axles offer significant weight reductions because a tag axle weighs less than a driven axle. In addition, the full configuration involves removing the inter-axle differential and associated inter-axle driveline components, as well as one differential gear set. A small amount of weight is added back in for load shifting and anti-spin measures. Overall weight reduction is in the 400-450 lb. range.
Including all load shifting and electronics, 6x2s are on a par with 6x4 axles
The fact that the 6x2 configuration allows for a reduction in the total number of driveline components should lead to an overall reduction in maintenance costs. There should be less vibration complaints and fewer U-joint lubes. Overall savings is estimated at $100 per year.
An overlooked benefit of 6x2 axle technology is that it might give the truck additional stability and control when operating in slippery or poor road conditions. With a 6x2 configuration, the tag axle cannot spin out because it is not powered by the engine. This means there will be some level of lateral force available to keep the vehicle stable on its desired path, reducing the potential for a jackknife event initiated by wheel spin.
The biggest concern surrounding 6x2 axles is loss of traction or tractive effort. Many of the situations where traction loss may be noticed with a 6x2 system are situations that should be avoided by vehicles no matter what the axle configuration:
• Deep snow
• Deep loose gravel
• Heavy ice
• Parking lots full of pot holes
Traction shortcomings of 6x2 axles can be mitigated with the use of load shifting technologies to increase weight on the drive axles at low speeds. The concern about traction is perceived to be a bigger challenge than it actually is.
Fleets running early versions 6x2 tag axle configurations experienced accelerated wear on their drive tires vs. the same tires used on conventional 6x4 tractor tandems. Reported decreases in tire life range from 50–70% of the wear life on a 6x4 (i.e., one third to one half tire life vs. an equivalent 6x4).
Some tire manufacturers recently expanded their recommendations on the way 6x2 vehicles should be equipped to mitigate tire wear.
Switching to a truck equipped with 6x2 axles will require some driver training. However, the newer traction control and automated load transfer systems remove a great deal of the concern about proper operation of a 6x2 truck from the driver.
There is no clear-cut view of the effects a 6x2 configuration will have on a vehicle at resale. Fleets that have embraced 6x2 technology indicated that they have buyers interested in purchasing their used trucks. Others believe that 6x2s will sell for upwards of $3,000 less than a comparable 6x4 tractor.
The common belief is that the resale value of 6x2 is rising, as the technology is better understood.
The study team identified three generations of 6x2 axles
Generation I: 6x2 with tag axles, no load-shifting technology, and manual differential locks
Generation II: 6x2 with tag axle, manual or automated load shifting, traction control, engine parameters adjusted to reduce low speed, clutch engagement, and engine brake torque
Generation III: 6x2 with liftable pusher axle, automatic load sensing/load shifting, traction control, and engine parameters to limit low speed/brake torque
To achieve the best fuel economy with 6x2 axles, fleet purchase them with these other components:
Tire manufacturers have recently expanded their recommendations on the way 6x2 vehicles should be equipped.
A Decision Guide summarizes the study findings to assist fleets in making decisions about 6x2 axles.
The Payback Calculator estimates the payback in months for end users who adopt 6x2 technology. Fleets input data into the form and the calculator uses that data along with information gathered by the study team to quantify the benefits and consequences likely to be experienced by the fleet in terms of upfront costs and year-over-year costs.
Currently six suppliers make 6x2 axles.
Major study conclusions include: