Axle Gear Ratios
Choice of axle gear ratio is a matter of vehicle application contingent on load weight and duty-cycle. Low gear ratios are used in vehicles to overcome a lack of torque from the engine and lack of strength in the transmission. A weaker drive train requires lower gear ratios. As today’s diesel engines produce more and more torque and transmissions improve, gear ratios are decreasing. A rear end ratio of 3.31:1 is now available for a diesel engine truck capable of a Gross Combined Vehicle Weight Rating (GCWR) of 25,700lbs. This includes the truck, payload, and trailer. A less tangible factor is the duty-cycle of the vehicle. An F250 that tows a travel trailer 500 miles a year is far different from a work-truck that operates 12 to 24 hours per day loaded to full capacity. Lower gear ratios reduce strain on the system and increase longevity in heavy use, high mile vehicles.
Engineers for F550 and Ram 5500 trucks have determined that a 4.88:1 gear ratio is ideal for the heaviest duty work trucks. They are designed to be busses, tow trucks, moving vans, utility trucks, dump trucks, heavy-haulers, etc. covering many miles a year hauling heavy loads. The Gross Combined Vehicle Weight Rating (GCWR) of a 2019 F550 is 40,000lbs all day, every day.
Considerations for selecting the best gear ratio: An F550 with 4.88:1 axle ratio on Single Wheel Conversion 41″ tires has an equivalent ratio of 3.94:1.
- A Brush Truck or Camper will weigh 19,500lbs at maximum load – half the GCWR of a fully laden F550 and 6,000lbs less than GCWR of an F250 with 3.31:1 gears.
- A 3.94:1 ratio is between the common 3.73 and 4.10 ratios with 31,000lb and 32,000lb GCWR respectively.
Conclusion: Most Single Wheel Conversion Brush Trucks and Campers will operate at a very light weight relative to GCWR of comparable work-truck applications. They will also see a relatively light duty-cycle not being run 12 to 24 hours a day, 365 days a year heavy laden. All considered, most Single Wheel Conversion trucks will live an easy life.
The factory 4.88:1 ratio is well within the operating parameters of this application.
Topping off the truck is an extra-wide bumper compensating the increase in front track width. The bumper extends past the fender flares to fend off fence posts, trees, and other obstacles jumping out along the way. At the heart of the bumper are the same features found on standard Buckstop bumpers including winch mount, tow hooks or mount points, trailer receiver, latching winch access door, built-in light mounts, and several options for built-in sirens, speakers, and monitor.