Flush Topper adds 2.1mpg at 70mph in a Gen 1 4x4 Tacoma

Speed/Load/MPG Tests were done on flat straight away sections of the highway. Readouts are from a calibrated Ultra Gauge.

Vehicle:
1997 Toyota Tacoma 3.4L 4x4 DLX Xtra Cab



Testing Protocol:
A-B

Route
62.1 Miles Each Direction

Trip A (Without Topper)

20 Minutes Warmup (Driving to start location)
Ambient Temp 32f
Intake Temp 56.2
Engine Coolant Temp 192.2

Speed MPG Load RPM
45mph 30.0 28.2 1800
50mph 29.2 28.2 2000
55mph 28.5 29.8 2150
60mph 25.9 32.9 2400
65mph 24.8 34.5 2600
70mph 21.8 38.0 2900

Total trip mpg = 25.0
Trip Average Speed = 53.2mph
Total Time = 1:14

Trip B (With Topper)

Ambient Temp 41f
Intake Temp 70.4
Engine Coolant Temp 192.2

Speed MPG Load RPM
45mph 32.7 26.1 1775
50mph 32.2 26.3 1975
55mph 29.9 28.0 2075
60mph 27.3 31.4 2350
65mph 26.5 32.2 2525
70mph 23.9 35.7 2800

Total trip mpg = 27.3
Trip Average Speed = 53.7mph
Total Time = 1:12

Improvement at 70mph = 2.1mpg
Trip Improvement = 2.3mpg

Just a quick coefficient of drag reference based on T-100/Dodge research. The lower number indicates lower drag coefficient.
*Flatbed ------------------------- Cd 0.668
*Pickup bed (open)---------------- Cd 0.44
*Full tonneau --------------------- Cd 0.415
*Suburban type roof (flush cap)---- Cd 0.39
*GM' Half-tonneau -----------------Cd 0.357
*Complete boat-tail -------------- Cd 0.12

 

now do it in reverse order. also, one tank of gas isnt that great of a indicator. but still need to see.

 

This isn't based on a fill up. This is based on instant readouts from my Ultragauge. But I will likely do an A-B-A test run in the future for further verification.

 

based of of instant readouts? then this is the most inaccurate test ever. the Instant reading isn't very accurate unless you somehow are managing to take the measurements at the EXACT same spots. Which is very unlikely. just a small incline or decline will have a huge impact on the instant read out.

Honestly. unless your getting 12mpgs or lower all the time. THe truck is running like normal and there is nothing to worry about. only rated for 15-18 anyways.

 

The accuracy of the instantaneous intstrumentation is accurate to itself in relation to the speedometer/tachometer. I made great effort to take samples from all very flat straight away highway stretches without traffic. The point of the test is to prove the theoretical aerodynamic improvements that should come from the addition of a topper vs. Open bed. All things being equal one should expect roughly 2+ mpg increase at highway speeds. Thanks.

 

Those are also pictures of an Xtracab, not a Double Cab...

 

Ummm, he mentions it is a dlx x-tra cab. Am I missing something?

 

pretty sure mythbusters covered this one; but did you buy the shell new or used and where? did you color match it or thats the stock black it came with? Love it, whether she tests dirty or not..

 

Edited

 

Thanks. I got it used from the original owner for $150 ( not who I bought the truck from) It's a color matched century topper. I like it allot

 

I spent a whole winter tracking my fuel mileage before and after i put my topper on and my mpg dropped. Went from 18.2 down to 15.4. no ultraguage just full fuel ups and figuring the mileage out that way. When i take the topper off put on my fiberglass tonneau cover it it went up to 16.5. Now with warmer weather it's starting to climb up a little. No one i know has ever gotten better gas mileage from adding weight to their vehicle. my truck is an 02 2.7 liter xtra cab. i would track each fuel up for the next ten months and see how it is. Mythbusters did the whole wind resistance episode and debunked the bed cover for better gas mileage theory.

 

Thank you, my apologies!

 

The warmer temps on the way back likely had a lot to do with your MPG.
Also, did you have any wind at all?

 

Thank you for posting this OP.

 

I did a four tank test doing the exact same commute as I always had done.

Best MPG I got was without a topper, tailgate up and bed completely empty.

Averaged 24.4 MPG over those four tanks.

 

Probably has more to do with winter gas vs non-winter gas.

 

my fuel mileage always drops in the winter. I don't deny that. I just had more noticible drops when i put a two hundred pound topper on it. My numbers are over a two winters so far. First winter was nothing which i got the most mpg. then threw the topper on and watched my mpg plummet and finally put my tonneau on and they went back up a little. still bad but better.

 

Not a windy day. I agree that ambient temps made a slight + difference, but they weren't significantly higher.

The 150 pounds addition of the topper would not likely be noticeable in any way at highway speeds, although one could notice a difference with city type driving.

The reduction in drag estimate of 12% (.44 down .39) should lead to a 6% reduction in fuel consumption at speed, and this lined up with the real world results of this test.

 

By those drag coeff numbers,,my flush mount old Brahma has drag like a open bed gate up,,when at speed. The kicker is the extra weight which yanks mileage away.

 

There's your difference.

And agreed... 60 miles is not enough for a valid test any more than when Mythbusters does the same thing with a measured gallon of fuel.

Also, was the wind speed and direction consistent? That makes a huge difference.

There's a reason that EPA gives us one number, and reality is all over the map from driver to driver and even tank to tank.
I drove my truck for 4 months, including a trip to Texas, before I got the shell. I saw no noticeable change in fuel economy. CERTAINLY not a 2mpg improvement. I got 23-26 those first 4 months, and I get 23-26 now.