Mack has combined its Super Econodyne spec’ with a direct drive version of its mDrive Automated Manual Transmission, boosting fuel economy by as much as 1%. The option is designed for trucks with Gross Combination Weights of less than 80,000 pounds and remain in top gear for most of the time.

Super Econodyne ratings were previously limited to overdrive versions of the transmission, but numerically lower rear axle ratios have made the direct drive version possible, Mack says. The 1% even builds on top of the 3% already delivered by Super Econodyne packages on their own.

The direct drive mDrive has a numerically higher top gear ratio, but realizes fuel efficiency gains through lowering parasitic losses. Torque is not transmitted to the countershaft while in top gear. The input and output shafts are essentially locked together, Mack explains.

The application works best on flat terrain when drivers are traveling at constant speeds.

Super Econodyne ratings integrate MP7 or MP8 engines with an mDrive transmission, enabling lower engine cruise speeds. Mack engines with the Super Econodyne rating cruise at about 1,150 rpm, which is 200 to 300 rpm less than a typical highway cruising speed, delivering a 3% improvement in fuel economy.