65 vs 70

[StRanger7032]

Years ago, I did a little MPG experiment with my Subaru Outback. I drove the same road, in the same direction, with the same wind and temperature, at 70 MPH and then again at 65 MPH. I compared the MPG with the on-board calculator and by good old fashioned math at the pump. The result: 24 MPG at 70 MPH and 28 MPG at 65 MPH. The on-board calculator was pretty much in line with the true calculation.

Last week, I did the same thing with my 2011 SR5. The experiment involved a 152 mile drive with identical conditions just like the last one. The gas was the same, as well. The results shocked me. I got 19.9 MPG according to the on-board calculator and 19.6MPG by math at 70 MPH. When I slowed down to 65 MPH, I got 24.4 MPG according to the on-board calculator and the same by math.

The cruise control was set for my experiments, only coming off to slow down for towns with lower speed limits and to accelerate back to highway speed. The test was done on relatively flat Texas highways with the air temperature in the mid 90s. Sure, you would need a dynamometer or at least a track to perfectly replicate conditions, but I think I came as close as possible for real world driving. By the way, I'm running stock P-rated tires and no lift, with only cosmetic mods.

My conclusion: 24 MPG+ is actually possible, even with E10, as long as you can control your right foot.

 

[Quentin]

Yup, I've gotten 24mpg over a whole tank by driving at 65mph through Ohio. The brake dive isn't bad if you are looking ahead and off the throttle going toward stop signs/lights, too.

 

[Qjake]

I'm lucky if I get 16 now nevermind 19 or 20 (which I never got either before lifting) but it's still better than my '09 DCLB Tacoma I traded for it. Honestly though I didn't buy the 4Runner for it's fuel economy and admit my truck loves to do 75+ :biggrin2:

 

[Stifler]

I guess I am th eonly one that doesn't care enough about MPG do waste hours of my life "experimenting" I get 390 miles per tank.... good to go

 

[1engineer]

Very good experiment! You have loosely proven the theory of drag! I will not post the formula but here is a good lesson to learn:

"Note that the power needed to push an object through a fluid (yes, air is a fluid lol) increases as the cube of the velocity. A car cruising on a highway at 50 mph (80 km/h) may require only 10 horsepower (7.5 kW) to overcome air drag, but that same car at 100 mph (160 km/h) requires 40 hp (30 kW). With a doubling of speed the drag (force) quadruples per the formula. Exerting four times the force over a fixed distance produces four times as much work. At twice the speed the work (resulting in displacement over a fixed distance) is done twice as fast. Since power is the rate of doing work, four times the work done in half the time requires eight times the power."

The take-away here is this: Doubling your speed requires 4X the power and the more power you use requires a proportional amount of fuel. Now, understanding that, the faster you get there (acceleration) the more fuel is required.

If you guys want the formula(s) I will be happy to post and explain.

Now, don't let anyone kid you about not wanting better fuel efficiency. Would anyone want a 4Runner if it got, oh, say 3 mpg when it's competition was getting 20 mpg? I don't think so. Most everyone on here that modifies their 4Runner knows that the efficiency goes down as weight and mass get added. It's still tough to break the laws of physics.

Very good post!

 

[453030]

Excellent post. Thanks for reporting your findings. Great avatar too.

 

[philsey]

I guess I am th eonly one that doesn't care enough about MPG do waste hours of my life "experimenting" I get 390 miles per tank.... good to go

I agree ... if this experiment takes "hours off your life", you probably are way over your head and you need to concentrate on just keeping it in the correct gear.

 

[philsey]

@OP. Good post. I have conducted very similar experiments with the same results.

I've even seen 25 mpg just poking along at 60 mph. I have also observed that mileage of the brick-like 5G is pretty susceptible to headwinds.

 

[philsey]

.....
If you guys want the formula(s) I will be happy to post and explain.
......

Double-Dog Dare Ya - but keep it simple enough so that stifler can play too, OK?

 

[1engineer]

Double-Dog Dare Ya - but keep it simple enough so that stifler can play too, OK?

Simple:

Drag Equation
Fd=1/2p*v*v*Cd*A
Where
Fd= Force of Drag
P=Density of Fluid (or air)
v= Speed of object relative to fluid
Cd= Drag Coefficient (.25-.45 for typical vehicles)
A= Reference Area

once you solve that then you solve

Pd= 1/2*P*v*v*v*A*Cd

This will give you power required to overcome drag.

 

[Antman]

Simple:

Drag Equation
Fd=1/2p*v*v*Cd*A
Where
Fd= Force of Drag
P=Density of Fluid (or air)
v= Speed of object relative to fluid
Cd= Drag Coefficient (.25-.45 for typical vehicles)
A= Reference Area

once you solve that then you solve

Pd= 1/2*P*v*v*v*A*Cd

This will give you power required to overcome drag.

This, by the way, is what 1engineer named his truck.

 

[Myron]

Simple:

Drag Equation
Fd=1/2p*v*v*Cd*A
Where
Fd= Force of Drag
P=Density of Fluid (or air)
v= Speed of object relative to fluid
Cd= Drag Coefficient (.25-.45 for typical vehicles)
A= Reference Area

once you solve that then you solve

Pd= 1/2*P*v*v*v*A*Cd

This will give you power required to overcome drag.

1engineer takes all the ribbing for this, but clearly others enjoy his posts. I'm an engineer too - keep on keepin' on 1engineer. Are there others of us on this board?

To the OP - great post. I love doing experiments like this too.

Myron

 

[CraigRoberts]

Could 1Engineer come out with some mods to reduce drag? Maybe a hybrid battery system too?

 

[angrydog]

1engineer takes all the ribbing for this, but clearly others enjoy his posts. I'm an engineer too - keep on keepin' on 1engineer. Are there others of us on this board?

To the OP - great post. I love doing experiments like this too.

Myron

+1 I'm a young engineer and enjoy how 1engineer owns people with actual theory which no one can really argue with other than the occasional num.nut. E=mc^2 bishes!!

 

[StRanger7032]

Thanks for the support! I tried to keep everything as scientific as possible. I honestly thought someone would rip me apart for this post. Of course, I did have a separate reason for making two 152 mile trips. It would be pretty illogical to waste 304 miles worth of fuel for no other reason than to prove better gas mileage at lower speeds.

 

[JB.]

Thanks for the support! I tried to keep everything as scientific as possible. I honestly thought someone would rip me apart for this post.

On the contrary.

With all the posts like (and I think this is my favorite) "I ran brand X oil for 60,000 miles with no problems" anything even approaching sound logic or real experimentation is waayyy welcome in my book.

Good post.

 

[philsey]

..... Of course, I did have a separate reason for making two 152 mile trips..

Reasons, I'm guessin'. :girl:

 

[1000MPH]

While I have tremendous respect for the field, I've worked with too many engineers with little common sense or real world experience. Think "Zen and the Art of Motorcycle Maintenance" or the TV show "Big Bang Theory"