Four years ago, Bruce Stockton asked a group of drivers and technicians at Joplin, Mo.-based CFI to inspect a new truck. After the inspection, the group became a forum discussion about how to cut the weight and cost of vehicles.
A couple of drivers made the same observation. The truck held 240 gallons of fuel in two 120-gallon tanks. The drivers said they were adding only between 80 and 100 gallons of fuel at each stop. Intrigued, Stockton looked at the fleet’s fuel-purchase data.
The driver observations turned out to be very astute. In the overall fleet, the maximum fill was 120 gallons, and the average was just more than 80 gallons per stop, Stockton says.
By reducing its tank capacity to 200 gallons, CFI – acquired by Con-way last year – cut 106 pounds of metal and 208 pounds of fuel from its trucks with zero impact to its service levels or driver routes, says Stockton, vice president of maintenance and asset management for Con-way Truckload.
Fuel tanks were just the beginning of Stockton’s new dietary plan for equipment. He also removed the extra bunk in the cab (84 pounds), used a lighter suspension system (53 pounds) and removed the quarter fenders (55 pounds). In total, tractors shed 673 pounds, and the purchase price came down by 2 percent. The fleet also trimmed another 400 pounds from tractor weight by running wide singles for drive tires.
In addition to cutting more than 1,000 pounds from its tractors, Con-way Truckload reduced its trailer weight by 1,000 pounds by spec’ing wide singles, composite wall plates and laminate flooring. Its gross vehicle weight is now 31,500 pounds, with 18,500 for the tractor and 13,000 for the trailer. The average load for Con-way Truckload is 30,000 pounds, Stockton says.Weight is just one variable, and some others are more significant, but despite the impact of 2007 engine emissions technology, Con-way Truckload’s fuel economy has held steady for the past four years.
Stockton estimates that every 1,000 pounds of weight removed increases fuel economy by almost one-half percent. Multiplied by Con-way Truckload’s 2,700 tractors, the fuel savings are significant. A scientific formula, courtesy of Kenworth, provides a way to calculate fuel savings attributable to weight reduction. It assumes a given rolling resistance for tires and for engine efficiency, expressed as a ratio of fuel consumption to horsepower output.
Suppose a 100-truck fleet averages 125,000 miles per tractor per year and that diesel averages $4.50 a gallon. According to the formula, a 1,000-pound reduction in weight would generate annual fuel savings per truck of $437.50 or $43,750 overall.
During a soft economy, carriers can’t always be selective in which loads they haul. For truckload carriers, shipment weights vary between 30,000 and 53,000 pounds. Given high diesel prices, it may make sense to incorporate a new metric, ton-miles per gallon, into your operations to better understand the impact of weight on fuel costs. Some truckload carriers even may start factoring shipment weight into their pricing.
For the industry, such a scenario not only is possible, but probable, Stockton believes. “A number of carriers will say it is not worth it unless we get paid for it.”
Estimating fuel savings from weight cuts
Annual fuel savings = [(Weight Savings) x (Tire Rolling Coefficient) x (BSFC) x (Miles/year) x (Fuel Cost/gallon) x (Number of Trucks)] / (Conversion Constant)
- Tire Rolling Coefficient = 0.006, the standard coefficient for fuel-efficient radials.
- BSFC = 0.35, the industry standard for Brake Specific Fuel Consumption (measured in lb/hp-hr).
- Conversion Constant = 2,700, for the all-English units used in this equation (pounds, miles, horsepower).