$5 DIY Half-tonneau

[SCNTN]

Just thought I'd share my latest little project. I found an aluminum-framed dry erase board at a garage sale for $1. It is 36" x 60", the exact dimensions I needed for a half-tonneau. So, I picked up a few nuts and bolts and a can of spray paint for $4. Then I fab'd a few "clamps" out of some one-by. I took the marker shelf off of the board and then reattached it backwards, forming a nice horizontal support for the front of the cover. The top of the tailgate supports the rear. One of the clamps didn't hold up so well, and will need to be remade. Other than that, looks pretty darn good!

[Frank Lee]

Nice repurposing

Although if that one clamp failed, I'd be worried about the others. I'd find some metal to do that job, or a different, beefier geometry if you want to stay with wood.

And if you like it and decide it's a keeper, perhaps some form of waterproofing will help it's longevity.

[SCNTN]

Yep, the whole thing was mostly an experiment. It is made of laminated MDF, not an ideal all-weather solution. It has rained here for the past few days, and surprisingly I haven't noticed any water penetrating the wood. As for the clamps, I had plenty of scrap wood lying around and just used what I had available. I have some scrap 1/2" EMT in the shed - I think I'll try to flatten and weld some of that into a more durable clamp.

As for results, it's hard to determine any FE gains with all this rain. However, watching the rear-view mirror I can see the aero effect at certain speeds by how the rain blows. It appears that most of the air flow is coming over the side of the bed rather than straight back from the cab as I would have expected. Imagine a diagonal line from the forward corners of the tonneau, going diagonally toward the center of the tailgate.

One other little detail that I realized during construction was that the bed of the truck actually tapers rearward from the cab to tailgate about five inches. I had always assumed this was a perfectly square box. I guess GM did put a little effort into aero after all...

[Smurf]

Yeah, that's a little known feature of S10/Sonoma beds, a slight taper on the slabsides. I have a full roll-up tonneau, but I'm interested in what kind of gains you can achieve with a half-cover.

[SCNTN]

I haven't done a true ABA test here, but apparently something isn't right with my design. Over the last two tanks my FE has dropped about 3 MPG. I have noticed that maintaining 55 MPH sacrifices a few MPG... typically at that speed, I'll average about 33 MPG, but with the half-tonneau that has dropped to about 29-30 MPG. My last tank (with fair weather) was 402 miles @ 16.4 gallons, about 24.5 MPG. I removed the cover right after filling the tank this week, and so far I'm back up to about 33 MPG highway. Rather disappointing...

[Tesla]

Originally Posted by SCNTN

I haven't done a true ABA test here, but apparently something isn't right with my design. Over the last two tanks my FE has dropped about 3 MPG. I have noticed that maintaining 55 MPH sacrifices a few MPG... typically at that speed, I'll average about 33 MPG, but with the half-tonneau that has dropped to about 29-30 MPG. My last tank (with fair weather) was 402 miles @ 16.4 gallons, about 24.5 MPG. I removed the cover right after filling the tank this week, and so far I'm back up to about 33 MPG highway. Rather disappointing...

Bummer, yes, but if it were me it would eat me up not knowing why.

Two possibilities, your FE checks were wrong because of weather or other factors or the 1/2 cap really did make FE worse.
I would run a few tanks without it and then try it again and see if you get the same effect, if so it may be it was just a bit too short to break the vortex and instead just captured it like a parachute.

There is a benefit with 1/2 caps and more with full caps in general, but the improvement is often overstated, I think drag reduction is somewhere between 5-10% and this then translates to 0-5% on FE, this is low enough to be lost in daily variations and error.