“Today’s emission-controlled engines are heavier. I will need the weight savings of a 6x2 to offset some of that increased weight.” 

Fleet Owner

Executive Summary

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.

2014 Report

Introduction to 6x2
Technology Description

​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

Available Systems

Common Fleet Strategies

To achieve the best fuel economy with 6x2 axles, fleet purchase them with these other components: 

  • Single wide-base tires on the drive axle
  • Ribbed low-rolling resistance wide-base trailer tires on the tag axle
  • A direct-drive transmission
  • A gear fast, run slow rear-axle ratio approaching 2.50 and filled with low-viscosity synthetic lube

​Tire manufacturers have recently expanded their recommendations on the way 6x2 vehicles should be equipped.

Decision-Making Tools

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.

Manufacturers

Currently six suppliers make 6x2 axles.

Conclusions

Major study conclusions include:

  • Drive tire wear on 6x2s will not achieve parity with 6x4s.
  • Fleets that take a systemwide approach and implement the full Generation II “package,” including load-shifting technology, traction control, and engine parameters to limit torque in low gear, at clutch engagement, and under engine braking, have a much better chance to realize the ROI potential of 6x2s.
  • Good and consistent driver communication and training is critical with this technology. 
  • The baseline (traditional 6x4 systems) is also improving. High-efficiency drive axles reduce the potential efficiency gains of a 6x2 system, albeit at a greater cost.
  • Residual values for 6x2s remain a problem.