There are many articles and forum discussions about the mileage benefits (or lack thereof) of a tonneau over a truck bed. We wrote about the topic almost two years ago - which is about the same as two generations in blog years - after a company called Snugtop did some tests with their tonneau covers and bedcaps and some fulllsize trucks from Dodge, Ford and Chevy and came away with good news. Of course, that was a company testing their own products, so skepticism is in order, but they did find a 1.3mpg improvement at 45mph.
In early 2007, SEMA took a look at the tonneau-saves-gas argument and came away with data that showed a pretty good improvement in the coefficient of drag of between 4.2 and 7.8 percent. That certainly sounds good, but Tundra HQ called BS on that pretty solidly, but figured that a 1mpg improvement could be had if the truck were going 85mph, but at lower speeds the efficiency gains would be quite reduced.
In any case, based on the the guesstimate that a snug tonneau could save 1mpg, I did some calculations for a 2006 Toyota Tundra. Coincidentally, that just happens to be the truck that my brother has - lucky, huh? The Tundra officially gets 14/19 mpg city/highway, so every little bit helps when we're talking about $4/gallons of gas. Since my brother lives in Miami, were people drive like maniacs and highways speeds are not exactly common (even on the highways), I used 16mpg as his baseline. If fuel costs $4 a gallon, which it will for the next five minutes, then each mile in this truck costs 25 cents, right? Prices for tonneaus vary, but here's one for $ 740 that seems like it would do the trick (note: I have zero history with that site, it's just something that Google turned up). If he never sat in traffic (ha!) getting zero mpg, how long will it take to earn back the cost of the tonneau? Follow me past the jump to find out.
Well, each time he drove four miles at somewhat higher speeds he'd save a dollar (again, assuming that 1mpg improvement). $740 times four would take 2960 highway speed miles, not exactly an unreasonable distance before the bed cover starts saving him money. ( UPDATE: I proved I'm not great at math with with post, and these numbers are wrong. See reader comments below) Of course, with the poor aerodynamics of the Tunrda to begin with, whether or not that 1mpg ever materializes is questionable. But even if it's just a half a mile per gallon savings, the tonneau will start to pay for itself after around 6,000 high-speed miles. Of course, using some of the many, many smarter driving tips could probably result in greater fuel savings without buying a new piece of equipment, but keeping your tires properly inflated and not driving like a rabbit on speed will not provide the side benefit of keeping your gear dry and safe from wandering hands.
Now, before you use these numbers to decide whether or not a tonneau is right for you, know that there is a lot to keep in mind that will affect your own situation. Hard tonneaus weigh something, which can offset the benefits of reduced drag. Also, if you opt for the lighter soft tops, then any flapping ends can wreck havoc on the drag, which is also bad. Tundra HQ also calculates the math using estimated time spent per day of driving instead of miles driven, and comes up with some pretty lengthy payback times (but their numbers were done using $3.50 gallons of gas). Lots to think about before plunking down some hard-earned cash for a bed cover. Of course, as fuel prices continue to rise, as they likely will, even those 1/2 mile per gallon improvements will start to look pretty good.
But what about you? If you drive a truck - preferably, if you've been driving pick-ups for a long time - have you ever noticed getting better mpg numbers with a covered bed? Are you sick of hearing this myth (if that's what it is) repeated over and over? At what fuel price would you consider getting a tonneau, even if it's only going to help a smidge?