Tonneau Efficiency Data Collection

[LightningShow]

It’s funny, as much as I don’t practically care much about the outcome here, I have been thinking about this - and something came to mind

I went and google-searched pickup truck class entries in the various Bonneville Salt Flats classes for land speed competition - and while my search wasn’t exhaustive, I didn’t find a single example without a tonneau (and they aren’t adding that weight for storage)

that research includes finding the F-250 Super Duty that in 2011 broke both the top speed record for a B Production Diesel Truck as well as for a B20 bio-diesel truck too…… over 171mph btw

that’s a hard tonneau back there

I would think these salt flat racers have thought through this and have some data to support their aero-choices

would be cool for an experienced salt flat truck class racer to come through and provide insight

EDIT TO ADD: I did find one comment reporting that a famous sale flat builder purported to have data that in fact the optimum setup was a tonneau that covered only 1/2 to 2/3 of the back of the bed, data-supported, something about creating low pressure area or some such - and I did see in my brief look one example of what appears to be a setup comporting with that

Wow, that seems like an amazing opportunity for Retrax to market a retractable cover that opens front to back! THE MOST EFFICIENT TONNEAU EVER.

 

[LightningShow]

My test plan is as follows:

1.) Choose a 40-50 mile loop starting at a DCFC.
2.) Charge to 80% at the DCFC
3.) Run the loop once to ensure the starting condition for the first test run is analogous to later runs ("conditioning run" data will be thrown out)
4.) At the end of the run, charge back to 80%
5.) Stop charging at exactly the point that the DCFC readout turns to 80% and record kWh delivered (I'll try to use the same station if I can)
6.) Repeat 3 more times, alternating between tonneau on/off.

I'll likely try to run this early on a Sunday morning so I can have relatively unimpeded travel. I'll also be able to drive faster/expend more energy. Hopefully that will amplify the difference (if there is one). I just identified a loop that's about 43 miles. Between travel and charging it should take ~1hr per loop. So, about 5 hours for 5 loops. Start at 5am, done at 10 am. Should be doable.

 

[LightningShow]

I want to know how much range the pie plate hubcaps will get me!

 

[ExCivilian]

I would think these salt flat racers have thought through this and have some data to support their aero-choices

Remember that, although it's about going the fastest, it's also about so much more. In order to go fast you gotta keep that rubber pressed against the ground and over triple digits things can start to feel a little bit "floaty" that I would hesitate to call pleasant.

Could even be something strange like a regulation or just to keep the bed from loading up with crap. Regardless, any data from years ago might not be particularly relevant given how much trucks have changed. The hood on your EV reminds me more of a car than a standard truck's. The tailgate now has a built-in spoiler. I'm not sure when the hood lines and tailgate were changed on the Ford but they didn't exist, as far as I know not even conceptually, when mythbusters did their tests.

As for hard vs. whatever mythbusters also has an episode where they determine the most aero vehicle is the one with a bunch of golf ball dents all over it, iirc so the hardest cover might not be the most effecient.

Here's a similar conversation regarding rake that might give someone a slight headache reading:
https://www.f1technical.net/forum/viewtopic.php?t=23240

So you're right in that a bunch of thought goes into these decisions...just not sure we're entertaining the right/relevant thoughts.

 

[cvalue13]

So you're right in that a bunch of thought goes into these decisions...just not sure we're entertaining the right/relevant thoughts.

certainly wasn’t intending to suggest that photos of “every salt flat truck has tonneaus” was definitive of anything - but instead only just as informative in one direction as it would have instead been in the other direction if no such trucks had tonneaus.

Just another uninformed “fact” to be squared against the weight of factors.

But as an aside since there seemed some miscommunication, this consistency includes trucks from the last few years (and for modified stock class, even our favorite 1/2 ton body styles). And, I’d think the issue of “weight” is more likely to be accomplished instead with further aero dealing instead with downforce generation. Both of which (modern 1/2 tons with downforce aero) exemplified below in “the world’s fastest pickup” (hit 254mph in 2021 season)

 

[PungoteagueDave]

Maybe we can argue over which brand of electrons give the best performance.

You do know that a full battery is heavier than an empty, correct?

 

[sotek2345]

You do know that a full battery is heavier than an empty, correct?

Of course! E=MC^2 and all that.

 

[ExCivilian]

Both of which (modern 1/2 tons with downforce aero) exemplified below in “the world’s fastest pickup” (hit 254mph in 2021 season)

The Jesel Team claimed that victory in a ~16 year old body design ('05 RAM).

One difference between those older designs and a more modern one is that our tailgates were straight whereas the newer ones are shaped to behave more like a spoiler:

The ICE F150 (and Lightning) also follow this design consideration:

Also note the lack of any gap between the body and bed compared to the Dodge.

A tonneau cover may be superfluous or even detrimental on a modern design.

 

[LightningShow]

My truck got 3.1 mi/kwh on the way back from the dealer after getting my tonneau! It wasn't installed, of course. The mere *presence* of the tonneau improved its efficiency!

 

[LightningShow]

One difference between those older designs and a more modern one is that our tailgates were straight whereas the newer ones are shaped to behave more like a spoiler:

Yes, the trailing edge of the tailgate also has a fairly prominent lip, maybe 1/2" high? If I need to log a guess, the tonneau won't make a difference. Though, I also wouldn't be surprised if it has a negative impact.

 

[ryan]

Two problems make this a resource-intensive experiment --

1. If there was a big difference, we'd already know about it. I think it's safe to assume we're talking about a small difference.

2. There are a lot of variables, and I mean a lot, that affect mileage in bigger ways than a Tonneau could. Speed, acceleration/braking behavior, other vehicles affecting draft, wind, etc. You could probably even imagine a situation where the Tonneau would improve mileage and another where it could reduce it. Just so many unknowns.

For small differences with lots of uncontrolled variables, you need many more trials. Not just two trucks doing a single run. Many more, and multiple runs from each. Then you'll be able to calculate p values, etc.

 

[LightningShow]

Two problems make this a resource-intensive experiment --

1. If there was a big difference, we'd already know about it. I think it's safe to assume we're talking about a small difference.

2. There are a lot of variables, and I mean a lot, that affect mileage in bigger ways than a Tonneau could. Speed, acceleration/braking behavior, other vehicles affecting draft, wind, etc. You could probably even imagine a situation where the Tonneau would improve mileage and another where it could reduce it. Just so many unknowns.

For small differences with lots of uncontrolled variables, you need many more trials. Not just two trucks doing a single run. Many more, and multiple runs from each. Then you'll be able to calculate p values, etc.

Sure, but you need to start doing runs to understand how many you actually need. There will always only be so much you can do to control the variables unless you have funding to run the testing. It's meant to be a real world test, as well. If you need precise control of variables to see a signal then you already have your answer. Control the big stuff that's easy to control (speed, driving style, atmospheric conditions, route, charging, etc) and if that isn't enough to see a signal then it's not making a meaningful real world difference.

Also, I'm just doing this for fun, I'm not applying for a permit to construct a nuclear facility! If I make a run and see that I used 10% less energy with the tonneau on then the next run it was 2% more, I'd probably just rack that up to no difference. I'm trying to gain some insight without committing a large amount of time.

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