Tonneau Fuel Economy experiment

Please explain how the center of the tread is going to cup inward. Kinda goes against basic physics... things like. centripetal force. Do a search for "tire ballooning" or even just watch a topfuel rail go down the strip. Tire expand with speed, most notably at the center.

I do agree that a chalk test is marginal at best. Pyrometers are far better and really are the best way to set pressure. I've done multiple tests and and "over-inflating" most definitely will cause the center of the tread to be hotter than the edges. Funny thing, the most even temperature distribution occurred right around that door sticker pressure! (assuming stock size tires)

 

Yeah, and there have been other scientific studys that have shown otherwise. There's the wind resistance one link earlier in the thread. There's one by a University in Minnesota. For the less comprehensive scientific there's mythbusters... the list goes on and on and they don't all agree.

I think it varies greatly by the particulars of each truck. Long bed vs. short bed. Height off ground. Single vs. Access vs. Double cab. All of these things have an effect.

That's part of why I did the experiment myself. With such different results from different studies, I thought it was important to verify with my particular vehicle.

After the experiment I've thought that I bet it helps less and less with each passing year of truck models. As fuel economy becomes more and more important, even truck designers are putting their vehicles in wind tunnels and optimizing the flow. Once that's been done, any thing that messes with the flow, even if it theoretically seems like a good idea, may combat the things done with the original design and thus hurt fuel economy.

I'm still considering doing the mess tailgate experiment to see if that has an effect. My guess is no, but if Mythbusters says it helps, while everything else hurts, it's worth a try.

 

The mass of the sidewall is greater than the mass at the center of the tread, but it's more an aerodynamic/hydrodynamic issue. The tire spinning in free air on a balancer may indeed expand more in the center, but when pressed against a surface, the center of the tread does indeed cup away from the surface because the water/air can not be pushed out of the way.

It is very obvious in hydroplane tests, but the same thing happens on dry pavement. I haven't looked for online videos, but I saw films of this happening some 30 years ago when I was working in auto parts.

 

The tire pressure inside the door is only a recommendation, based on type and purpose of vehicle. The sidewall is the guage of maximum. When I bought new wheels and tires for my Mustang, the guy who supplied my parts, and builds race cars, when I asked about tire pressure, said the sidewall. If you aren't going for comfort, tbe more air will give you better performance. Just like on my mountain bike, the harder the surface, the more air. Gives less rolling resistance, and a stiffer sidewall means less body roll, or lean, thus less sideways inertia.

Going over the sidewall recomendation, however, isn't smart. Though there is allowances made for expansion due to heat, you risk a blow out. Sure, you might not, just as excedding the speed rating doesn't necessarilly guarantee shredding a tire. However, you've exceeded the maximum guaranteed safety rating, and the risk increases exponentially. That, and suffer a blow-out, and cause a fatal accident, and you're in for a world of liability hurt when they figure out you exceeded maximum rating. (And they will...I saw it on CSI once, so it must be true)

As for the tonneau, in statistics, there is something called statistically insignificant, which basically accounts for "margin of error". I'd call anything under 1mpg statistically insignificant. But then, I'm buying the cover to keep my crap dry.

One thing I have been curious about is the little tails they're putting on GMs and Dodges now, and if they're for mileage. Most guys I talk to agree they look odd, so I don't think it's for styling.

 

My scientific analysis over the last 3 years of driving my truck have led two conclusions:

1. The greatest way to increase mileage is to drive with a feathered foot.

2. If you are worried about pinching pennies on gas get a Prius.