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Old 02-21-2021, 04:33 PM   #1 (permalink)
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Ruint Taco - '19 Toyota Tacoma SR Double Cab
90 day: 23.5 mpg (US)
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40% Tonneau Cover on 2019 Tacoma

Today I did some A-B testing.

I wish I more time for this post, so I apologize in advance for no pictures right now. But I was so excited , I want share my results. To the average guy, this not going to sound exciting, but I know y'all will dig it.

Vehicle is 2019 2.7 four cylinder Tacoma with 4000 miles. The previous owner didn't drive it much.
It's a crew cab, short bed(5ft) 2WD base truck. Tires all inflated to 32 PSI.
No mechanical modifications have been made. Other than the cover which covers the last 40% of the bed, The only other mods was running boards/steps and aftermarket aluminum wheels.

Cover is made of 1/4 plywood and sits perfectly flush with the bed sides and tailgate. Weight is 15 pounds I'm guessing.

I live in Georgia and the weather this morning was 49 degree. Traffic was light and virtually no wind. The road was a four lane divided highway for most part. the fist and last .6 of a mile was a two lane road from my house to highway. The loop I ran was 7.3 miles, mostly level. Light traffic.

Speed on two lane road was 44 miles an hour, on four lane road speed was 64. I accelerated by flooring it till I got to 30, engaging the cruz and selecting the desired MPH( which you can do on this model, on other cars you can't). I did it this way to minimize the difference between runs. I also tried to brake at the same points. I let the cruz handle the gas once it was set.

I did 5 runs this morning. The MPG results are from the trucks built in gauge.

First I drove the truck for 15 miles at highway speeds to get it warmed up. It return 19.1 on this trip, mostly because of the cold start.

7.3 mile loop on fairly level road. Light traffic, so that had little effect. No wind. Only about 6.1 miles was at actual highway speeds, I would like to go on a longer loop in the future. The MPG results from these loops are not great because : A. truck isn't broken in , B. I wasn't hypermiling, I was trying to get repeatable test.


1st run with 40% cover -22.5 MPG
2nd run without cover, tailgate down-21.3 MPG
3rd run without cover , tailgate up-21.7 MPG
4th run with 40% cover 22.7 MPG
5th run without cover 22.00 MPG

The second run was a mistake. I forgot and left the tailgate down when I removed the cover. I decided to go with it after I noticed and see what the result where.

Average with Cover-22.6 MPG
Average without cover-21.85 MPG

Net results is .75 MPG gain with 40% cover.


Cost to build cover was about 50 bucks, because lumber is extremely high right now. I will post pictures soon. It looks pretty good, it 1/4 plywood with a 2X2 frame, painted with bed liner.

Estimated yearly savings for me driving 14000 miles and gas at $2.30 is $48.23 from this mod.

In a future post I will explain why I did a 40% cover, instead of 50%. I will also try a 50% cover in the future.

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Old 02-21-2021, 06:31 PM   #2 (permalink)
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Ruint Taco - '19 Toyota Tacoma SR Double Cab
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Ok, so I got some time. I want to explain why I did 40% coverage , instead of 50%. I looked at the original GM patient on the 50% cover. The test were done on a 1982 Chevy, standard cab, with 8 foot bed. I just happen to have a 79 Chevy with a 8 ft long bed. My truck is identical to the test truck in outside dimensions.

My thought the real secret is the ratio of the back of the cab height to the front of the cover. So I measured the cab height on the 79 truck. it about 44 inches. Half of 8 feet is 48 inches. So I used this ratio when designing my cover. Keep in mine my Toyota has an extremely short bed of only 5 feet.

I'm open to saying I could be wrong about this. Only way me to tell is to build a extension on my cover and do more A-B testing.

I also found a test done on a modern pickup, I'm sorry I didn't bookmark it. In that test they actually saw results but only covering last 12 inches of the bed. This was done on a modern crew cab short bed truck.

Last edited by Vwbeamer; 02-21-2021 at 08:20 PM..
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Old 02-21-2021, 06:37 PM   #3 (permalink)
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https://photos.app.goo.gl/Z2XzPtnpKwvGt92F9
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Old 02-21-2021, 06:39 PM   #4 (permalink)
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https://photos.app.goo.gl/BiPvu8js5Swti1LL6
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Old 02-21-2021, 08:53 PM   #5 (permalink)
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I've always wondered whether a front wall on the tonneau cover is necessary.

I saw one explanation that the air pressure needs to be transmitted back to the forward face of the tailgate. And another that it creates a rotating bale of air in the front of the bed which suggests a curved or angled front wall might be best.
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Old 02-21-2021, 09:13 PM   #6 (permalink)
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Yea, I'm not sure how it works, I think rotating bail of air. Just amazed that a simple piece of wood could lower drag.

Due to personal problems (2021 has been worse than 2020 for me), I am really limited on time to experiment with this, but I plan on doing more. I would like to see how a full cover would do.

I want to do some A-B runs on the interstate at 70+ MPH and with a 20 mile long loop. I also want to vary the length of the cover.
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Old 02-21-2021, 09:23 PM   #7 (permalink)
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Ruint Taco - '19 Toyota Tacoma SR Double Cab
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My goal is to get 26 MPG from this truck, which I inherited when my Dad passed away.
I coming from having a Jetta TDi and then a C-Max hybrid, so the 21 mpg this thing gets is a big shock. But I want keep it because it was my Dads and my kids like riding in the "truck".

I want to run a total loss on the charging system. To get current for the electrical system I want to mount a solar panel on the 40% cover, and have it charge a deep cycle battery. The deep cycle would charge the factory battery via a DC to DC convertor. I think cost would be 400 hundred, with a 2 MPG gain. I would use a Ardunio to control the system so that the factory alternator would kick in under braking or if the deep cycle battery voltage dropped below 12.2 volts

This should get me to about 24.5 MPG. I would tweek the front air dam and maybe lower truck to get to 26 MPG
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Old 02-22-2021, 06:36 AM   #8 (permalink)
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Ruint Taco - '19 Toyota Tacoma SR Double Cab
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link to the original GM patent

https://www.freepatentsonline.com/4573730.pdf
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Old 02-22-2021, 08:49 AM   #9 (permalink)
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Ruint Taco - '19 Toyota Tacoma SR Double Cab
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forum on pickup drag, post 11

https://www.gminsidenews.com/threads...mileage.11678/

" Interestingly, a partial 20-in. cover placed nearest to the tailgate did 88% as well as a full tonneau cover."
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Old 02-23-2021, 11:55 AM   #10 (permalink)
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Quote:
Originally Posted by Vwbeamer View Post

I want to run a total loss on the charging system. To get current for the electrical system I want to mount a solar panel on the 40% cover, and have it charge a deep cycle battery. The deep cycle would charge the factory battery via a DC to DC convertor. I think cost would be 400 hundred, with a 2 MPG gain. I would use a Ardunio to control the system so that the factory alternator would kick in under braking or if the deep cycle battery voltage dropped below 12.2 volts
Keep in mind lead acid batteries have poor cycle endurance and cost quite a bit of money over time if used that way (per cycle, LiFePO4 batteries are cheaper than lead acid). The alternator can be used not just when braking but also when the load on the engine is very low.

A solar panel tonneau cover is a good idea though :thumbsup:

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