Since fuel economy is an increasingly important concern in a time of escalating gasoline prices, industry-leading fiberglass truck cap and tonneau cover manufacturer SnugTop undertook an apples-to-apples comparison test to see how the aerodynamic enhancements offered by caps and lids affected gas mileage, compared to stock open-bed pickups.
The concept was to take three similarly equipped late-model trucks, including a Chevy Silverado, a Dodge Ram, and a Ford F-150, and test them under similar conditions, with and without caps or lids.
THE TRUCKS
THE CHEVY
The '06 Chevrolet Silverado Crew Cab with a 5.3L Vortec V-8 and automatic transmission had about 13,600 miles on the odometer. AAA calibration showed that for an indicated 5 miles traveled, the actual dyno-certified distance was 4.9178 miles, which left a correction factor of 0.98356.
THE FORD
The '06 Ford F-150 Extra Cab with a 4.6L Triton V-8 and automatic transmission had almost 8,000 miles on the odometer. AAA calibration showed that for an indicated 5 miles traveled, the actual dyno-certified distance was 4.9574 miles, which left a correction factor of 0.99148.
THE DODGE
The '04 Dodge Ram 1500 SLT Quad Cab with a 5.7L Hemi V-8 and automatic transmission had about 15,100 miles on the odometer. AAA calibration showed that for an indicated 5 miles traveled, the actual dyno-certified distance was 4.9280 miles, which left a correction factor of 0.98560.
Irwindale Speedway's own pace truck was offered up for testing purposes. Usually, there are a few dozen snarling race cars following it around the track. | 
The guinea pigs for the SnugTop mileage test were an '06 Ford F-150, an '04 Dodge Ram, and an '06 Chevy Silverado. The engines were 4.6, 5.7, and 5.3 liters, respectively. | 
AAA technician Paul Keen (in truck) and Laboratory Director Steve Mazor calibrated the speedometers and odometers of the test vehicles and helped set up testing procedures. |
The official track pump at Irwindale is calibrated for read-outs to the thousandth of a gallon. Sunoco 91 octane gas was used for the testing. | 
Fueling procedures (as used by AAA in its testing) consisted of filling the tank to three "clicks" of the nozzle. Irwindale's Joe DeFazio did all the fueling. | 
Each truck was outfitted with one of the Speedway's transponders, which helped monitor the number of laps driven and calculate actual speeds. Mike Atkinson did the installations. |
HOW THEY TESTED
In a perfect world, the tests would have been conducted in a totally climate-controlled environment, at speeds more accurate to highway travel, and with robots performing all the tasks. But, since that was virtually impossible, SnugTop did the best it could under the circumstances.
To avoid the pitfalls of trying to perform tests on city streets or highways, Irwindale Speedway's facility was offered by General Manager Bob DeFazio. Preliminary testing showed that a speed of 45 mph was about as fast as a factory stock truck could be driven consistently on Irwindale's half-mile oval without being affected by tire scrub in the corners. And to eliminate a variable of driver gas-pedal actuation, cruise controls were employed, exclusively.
One area that could not be tightly controlled was the "line" each driver took. However, all drivers were instructed to stay close to the line that's painted in the center of the track. Also, the fuel economy was calibrated from actual miles driven, so if one driver had a slightly more circuitous route around the track than the others, it didn't matter.
Prior to running the laps, the three trucks were taken to the Automobile Club of Southern California (AAA) Test Facility in Diamond Bar, California, and their odometers and speedometers were calibrated on a dyno by Automotive Research Specialist Paul E. Keen, Jr.
The trucks were fueled using the same parameters as AAA uses for its mileage tests, according to the facility manager, Steve Mazor; fill to the "click" three times in succession. All refueling was done at the same Irwindale Raceway pump, which reads fuel use to three decimal points and by the same person, Joe DeFazio.
Each truck was equipped with one of Irwindale Speedway's transponders, so lap data was fed into the track's scoring system and monitored by veteran NASCAR official Jack Buchanan.