Let’s face it, the words aerodynamic and pickup truck are rarely used in the same sentence. And for good reason. They are essentially incongruous (how aerodynamic is a brick?). However, all kidding aside, aerodynamics do play an important part in the performance and fuel efficiency of pickup trucks—especially in relation to the bed.
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One of the more hotly debated topics among truck owners is whether it’s best to keep the tailgate up, put it down, or even add a net. The second half of the equation is whether a pickup truck equipped with a tonneau cover or cap is more aerodynamically efficient than one with an open bed.
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Needless to say, this has been the subject of considerable conjecture. However, several years ago the Specialty Equipment Market Association (SEMA) conducted a thorough set of experiments at the AeroDyn Wind Tunnel in Mooresville, North Carolina—a facility favored by the NASCAR community, and put it all to rest. The SEMA study determined that there’s no advantage to an open tailgate or net, and that a fiberglass tonneau produced up to a 6.5 percent improvement in coefficient of drag (Cd) over an open-bedded truck.
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SnugTop, an industry-leading manufacturer of fiberglass truck caps and tonneau covers has also been active in this arena. In addition to supplying product for use in the SEMA wind tunnel project, the company recently conducted a real-time experiment at Irwindale Speedway near Los Angeles, where a Chevy, Ford, and Dodge pickup were run around the track at a steady cruise-controlled 50 mph for 50 laps and the amount of fuel consumed carefully measured. The trucks were tested with an open bed, and also with a SnugLid tonneau cover and SnugTop cap. As expected, the results verified the wind tunnel data; trucks equipped with caps and tonneaus obtained solid improvements in fuel economy over open-bedded trucks. They varied from 4 to 10 percent, depending on the host vehicle and engine package.
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The 50-mph Irwindale test showed a covered bed to be more efficient than an open bed, but no discernable difference between the cap and the lid. So the logical follow-up quest became to see how an open bed, lid, and cap fared at serious speed.
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Enter the “Mojave Mile,” a unique speed contest held on the 12,503-foot-long runway at the Mojave Desert in SoCal. The idea was to take a high-performance pickup truck and see how fast it would go with an open bed, tonneau cover, and cap. The project was dubbed the “SnugTop Speed Showdown.” But what truck to use? Luckily, Steve Sanett, an automotive enthusiast/collector and vintage Porsche racer, offered up his pristine ’04 Dodge Ram SRT10 for the project. With its massive 8.3L V-10 Viper engine rated at 510 hp at 5,600 rpm and a whopping 525 lb-ft of torque at 4,200 rpm, the SRT10 is recognized as America’s most powerful production pickup, according to Wikipedia, which shows an SRT10 driven by NASCAR Truck Series vet Brendan Gaughan setting an American speed record of 154.55 mph on Chrysler’s test track.
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To make sure the SRT10 was operating at its peak potential, the factory exhaust was replaced by a Borla stainless steel cat-back system, all fluids (engine, transmission, differential) were converted to Royal Purple synthetic products, and the ECU was optimized through use of an SCT handheld tuner with a series of programs created by Torrie McPhail of Fast Parts Network. Needless to say, the Mojave Mile folks are strict about tire age and proper speed ratings, so the big Dodge was shod with a new set of BFGoodrich gForce T/A 320x40 ZR22 tires.
After a rookie qualifying pass, Sanett made two more runs with the SnugLid tonneau cover in place. They produced clockings of 140.2 and 143.0 mph, for an average of 141.75 mph. The tonneau was removed and two more runs made, and the average dropped well into the 130s. More importantly, driver Steve Sanett, who has ample track time at places like Daytona International Speedway, Road America in Wisconsin, and California Speedway, reported that the truck felt much more stable at speed with the tonneau than with the open bed.
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The bad news was that due to timing delays the crew was unable to make tonneau/cap switch and get the desired number of runs to produce true A-B-C speed comparisons. Moreover, it was evident that the gear ratios in the Ram’s six-speed Tremec T56 transmission and the 4.10 rearend cog were far from ideal for the task at hand. The Tremec has 2.66, 1.78, 1.30, 1.00, 0.74, and 0.50 gears. Just after Sanett shifted into Fifth gear the finish line quickly passed.
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The good news came in the form of “Phase Two” being conducted at the “Mojave Magnum” event where the course was a longer 1.5 miles and would allow some more speed to build.
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With a covered bed being previously proven more efficient than an open one, testing was focused on the tonneau versus a cab-high shell. With the extra distance to play with, the mighty Dodge clocked a best of 153.9 mph with the form-fitting SnugLid tonneau in the 1 1/2 mile “Mojave Magnum.” How would the SnugTop fare?
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Two runs were made with the SnugTop “Super Sport” cap in place, with speeds of 153.3 and 153.5 mph recorded. So the difference in top speed was only 0.4 mph—possibly attributable to the extra 100 pounds or so weight of the cap (mostly the glass) or changes in the wind. In all instances, the truck was slowly gaining rpm in Fifth gear, just shy of a shift into Sixth.
Conclusion? It’s a draw from an aerodynamic standpoint. Either a cap or tonneau cover appears to provide similar improvements over an open bed.
The “SnugTop Speed Showdown” was also an eye-opener to see how fast the 5,000-pound truck performed compared to the Corvettes, Vipers, Ford GTs, and Porsches that frequent the “Mojave Mile.” It isn’t often you get to see a stock pickup go 150-plus mph and the driver not get a speeding ticket! And it leaves you to wonder how our test truck would fare on a closed circuit track where it could get into Sixth gear. A Guinness World Record, anyone?
