The roll-top tonneau cover on the 2024 Tesla Cybertruck makes the car much more aerodynamic. We tested the Cybertruck at 75 mph while the top was open and closed. The second setup used 10% more energy. Our tests show that the Cybertruck’s real-world range drops from 250 miles to 225 miles when the top is open. When the top is closed, and the truck is driven at 65 mph, we expect the range to rise to 295 miles. It might surprise you to learn that the Tesla Cybertruck is shut off more than you think. The prototype had a flat nose that was changed to a softly curved front panel that helps air move across the front flanks. The front end was always going to be tough, though. Also, the front flares have been carefully shaped to create a small, purposeful swirl that will help the flow curve more smoothly around those too-sharp front corners. For the driver, at least, wind noise isn’t as crazy as you might think because the big wiper acts like a fence, pushing air over the top instead of letting it swirl down against the driver’s window. The Cybertruck’s underside is much smoother than any ladder-framed truck could ever hope to be. It has a few fairings and holes that let air flow over the lower control arms of the suspension. The Cybertruck’s back end looks sharp, but it fits the vehicle very well, which is the most surprising thing about its aerodynamics. The most aerodynamic form is on the back sides, which have a gentle taper like a raindrop. The sudden end of the tailgate is actually very good for aerodynamics. Wunibald Kamm (of Kammback fame) showed that a sharp cut-off would trick most of the air moving over such a body into continuing on a laminar path, which would lower drag more than a smoothly rounded design. We tested at 75 mph steady state with the tonneau open, closed, and both open and closed. This was done so that the air “captured” by the open bed could get out. Well, the Cybertruck’s roll-top tonneau cover is a must for all of this. We did tonneau-closed runs without wheel covers, too, to see what effect they had. Our 834-hp tri-motor Beast Cybertruck was on 35-inch all-terrain tires because it was windy. To avoid wind impacts, we tried the car in the above configurations around a 6.6-mile oval track. As we drove by a fixed point on the course, we also reset and wrote down the truck’s internal cumulative usage meter. We changed this number to kilowatt-hours per 100 miles because that’s how this type of usage is usually shown. The meter shows real-time usage with three numbers in watt-hours per mile. What did it lead to? Avg. use was 58.3 kWh/100 mi when the tonneau was closed and 64.2 kWh/100 mi when it was open. With the trunk lid open, our 250-mile range test result might have been only 225 miles since the car would have used 10% more gas. Since the door was reading 64.0 kWh/100 mi, opening it at this point did not make a big difference. When the tonneau was closed and the wheel covers were taken off, on the other hand, there was only a 1.7% loss: 59.3 kWh/100 mi instead of 58.3 kWh/100 mi. We did some of our runs again at 65 mph because aerodynamic drag goes up with speed. When the trunk lid was closed, the car’s energy use dropped from 58.3 to 49.3 kWh/100 miles. That means that it was used 15.4% less, which is equal to about 295 miles at 65 mph. It shouldn’t have been a surprise that our 65 mph bed-exposed run increased by the same 15.6%, requiring only 54.2 kWh/100 miles at 65 mph instead of 64.2 kWh/100 miles at 75 mph, since improvements in velocity-related aerodynamics are the same no matter the setup. The lesson of the story is to keep quiet. It works better, but the “benefit” of better vision from the inner rearview mirror isn’t as big as it seems because the view is limited and slot-like. The camera system works better than we thought. Slow down a bit if you want to increase your possible range even more.
