4WD Mechanix Magazine’s 2005 Dodge Ram 4×4 Ram truck with Cummins 5.9L diesel power has an aftermarket 4-inch chassis lift and 4.56 axle gears. To achieve peak handling, fuel efficiency and towing power, we set out to fine tune the overall “gearing” by selecting the right diameter BFG tires and a matching set of Raceline Avenger series wheels.
The Ram 3500 has 1,200 pounds of accessories and add-ons, including a HD winch and winch bumper, shell/cap, oversized tires and a 75-gallon auxiliary fuel tank. Axle gearing has been changed to 4.56:1 front and rear. BFG KO2 tires have served well with this package since the launch of the new KO2 tire design. The magazine’s Dodge Ram 3500 truck features a variety of upgrades and heavy duty accessories that have each added weight and load on the powertrain.
The 30′ Holiday Rambler Alumascape trailer weighs approximately 8,400 pounds loaded (wet) and over-the-road. The Raceline Avenger wheels and BFG KO2 tires are rated well in excess of the truck’s load carrying Gross Vehicle Weight (GVW) and GCWR for towing.
The Cummins diesel and fuel efficiency are closely tied to engine rpm. Our experience has the 5.9L 24-valve H.O. engine in its “sweet spot” for torque and fuel efficiency between 1,600 and 1,900 rpm. Hypertech Max Energy Stage 3 tuning presses the torque peak rpm up from the factory 1,600 rpm to a higher 2,150 rpm. Optimal torque/power range is now 1,600-2,150 rpm. We wanted this engine speed to match precisely with commonly used road speeds and trailering demands. Our target is maximum fuel efficiency and taking advantage of peak torque.
4.56:1 axle gearing and a DSI custom driveshaft meet the larger tire and performance demands. We have relied upon BFG tires since this truck was new, and the KO2 37″ x 12.50 x 17 tires offer a precise match for this axle gearing, the chassis lift and the engine’s peak torque.
Exceptional tire life is attributable to proper tire mounting, balancing, regulated tire pressures, tire rotation intervals and correct wheel alignment. Front wheel alignment is performed at the magazine’s shop to assure accuracy and consistency.
To fine tune with our aftermarket 4.56:1 axle gearing and 4-inch chassis lift, the best match is the BFG KO2 37″ x 12.50 x 17 tires. These tires are rated as a true 36.5″ diameter (mounted). For maximum performance, fuel efficiency and handling both on- and off-highway, we turned to Raceline Wheels and the Avenger-series 929M wheels. Proper tire mounting, careful balancing and the right tire pressures are also detailed in this HD video coverage! Join us at the forums for more details and discussion on Ram Cummins fuel efficiency, trailering demands and diesel tuning.
Below are charts with details on gearing and engine speeds at cruise highway speeds:
Click below for PDF versions of these charts: