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.

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.

THE RESULTS
The tests were conducted on a normal California day, between the hours of 11:30 a.m. and 3 p.m. The sky was overcast and temperatures remained fairly consistent at 78-80 degrees Fahrenheit. The wind was relatively calm.

First in line was the Dodge, which was filled and sent out on the test with 15,155 miles on the odometer. It was equipped with a SnugLid tonneau. The Silverado was next and hit the oval with 13,646 miles on the odometer and a SnugTop Cab-Hi cap covering the bed. Finally the Ford, equipped with a SnugLid fiberglass tonneau cover, hit the track, fully tanked, with 7,998 miles on the odometer.

After doing the requisite 100 laps with the cruise control set at 45 mph, the drivers made a pit stop and were topped off per AAA procedures. The Dodge got 19.38 mpg, the Silverado scored highest at 23.06 mpg, and the Ford squeezed out 21.30 mpg.

The pit stop also included removing the SnugTop cap and SnugLid tonneaus from the vehicles. Off they went with Irwindale Speedway officials Lester Boyer, Mike Atkinson, and Joe DeFazio at the controls.

When they returned and got topped-off, the mileage was calculated. The Hemi-powered Dodge showed the most significant differential, with a 1.32-mpg drop with an empty bed, followed by the Chevy and Ford.

Incidentally, Irwindale's race central calculated that the fastest truck averaged 45.241 mph for the 100 laps, and the slowest averaged 44.496 mph.

The best mileage gains were achieved by the SnugLid tonneau-equipped Dodge Ram. The Hemi-powered truck showed a 1.3 mpg improvement at only 45 mph. The Chevy did pretty well, netting a 0.5 mpg improvement. The Ford ended up stopping a lap down from the 100 and could not be calculated correctly and there was just no time left for another set of 100 laps at 45 mph.

THE FINAL WORD
What did we learn? Under fairly stringent testing procedures, we quantified fuel savings as high as 1.3 mpg. And that was at a speed of only 45 mph.

We know that the results of the testing would have shown even better improvements if the baseline had been 60 mph, instead of 45. Engineers tell us that aerodynamic drag increases with the square of speed. So, even though the increase in speed from 45 to 60 mph is about 30 percent, the drag would increase exponentially to just more than 75 percent. Now, there's a whole lot more involved here than simply mitigating increased drag through the aerodynamic enhancements offered by a truck cap or tonneau cover, but the bottom line is that highly credentialed engineers will agree that a test at a higher speed would likely produce additional increases in fuel economy. They just can't assign an exact number to the gain.

SnugTop has received solid feedback from customers who have claimed increases as high as 1.5 to 2 mpg after equipping their vehicles with the company's caps and lids. This pretty much corroborates the test results.

Of course, results will vary by vehicle condition, its equipment, and the type of driving done. But, it's a safe assumption that under normal circumstances, it's possible to save hundreds of dollars annually in fuel costs by covering up that empty bed with a cap or tonneau cover.

SOURCE
SnugTop
1711 Harbor Ave.
Long Beach
CA  90813
www.snugtop.com
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