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View Full Version : MPH vs MPG, a test this morning to find the best bang for the mph


problemchild
10-21-2011, 6:07 AM
I ran a test early this morning when there were no cars on the road. I have a local street near me that is 3 miles long and flat. There are no lights to turn red in the middle of a test. So here is what I found for my car at least.

Test conditions
Flat
No wind
64f
lights on
AC off
Heater off
Tires at 40psi
Radio on
Windows up
Reset trip at beginning of each test after cruise set to speed

Pass 1
35 mph = 39 mpg

Pass 2
45 mph = 39 mpg

Pass 3
50 mph = 35.5 mpg

Pass 4
55 mph = 31.5 mpg

Pass 5
47 mph = 36.9 mpg

So it looks like if I needed to maximize mpg (gas) bugging out I need to set my cruise at 45mpg. The rpm's were lower at 50 (1800)(gearshift) then they were at 45 (2200) but I guess the drag of the wind was causing it to get worse after 45.

OriginalDuplicate
10-21-2011, 10:15 AM
very cool test. What kind of vehicle is that?

I have been watching the cars market for awhile since my '01 corolla with 250,000 miles on it is about to die.

How clean was the air filter? I heard that can impact milage also.

Interesting to see that 45 is the best for mpg. I have always heard that you get the best around 55mph.

shooterfpga
10-21-2011, 10:27 AM
i get good mileage at 55mph, anything above that and it starts dropping fast. at 90mph its 3-4mpg.

d4v0s
10-21-2011, 10:49 AM
I did a similar test the other day in my exs dodge pickemup.

55mph was 15.5mpg
65mph was 13.7
90mph was 12.2

I was helping a friend move so i drove the same road (little over 17 miles one way) and decided to make it scientific.

Then we went to the mountains

all uphill over pine mountain averaged 5.5mpg.

This is a dodge quad cab 2500 4x4 with Hemi

In my ranger,

55mph was 24-25mpg (avg over several trips to the desert 220miles one way).

90mph stuck on the speed limiter almost the entire way is 13.7mpg almost on the dot every single time. Although this is also towing a few days worth of gear and a trailer filled with 5 bikes.

Joewy
10-21-2011, 11:39 AM
I get 25mpg on the east bound side of the I-80 and 15mpg on the westbound side....

Wind sucks...

problemchild
10-21-2011, 12:39 PM
very cool test. What kind of vehicle is that?

I have been watching the cars market for awhile since my '01 corolla with 250,000 miles on it is about to die.

How clean was the air filter? I heard that can impact milage also.

Interesting to see that 45 is the best for mpg. I have always heard that you get the best around 55mph.

I have an 2011 subaru forester 4 spd auto 2.5. Air cleaner has about 18k on it.

xrMike
10-21-2011, 2:29 PM
You guys are using your car's onboard computer or electronics for your mileage numbers, I'm guessing...

I've always wondered how accurate those numbers are. I can imagine a LOT of possibilities for error there. How do the electronics make their computation?

Joewy
10-21-2011, 2:37 PM
I have an 2011 subaru forester 4 spd auto 2.5. Air cleaner has about 18k on it.


Thats pretty good for that car......

shooterfpga
10-21-2011, 4:28 PM
You guys are using your car's onboard computer or electronics for your mileage numbers, I'm guessing...

I've always wondered how accurate those numbers are. I can imagine a LOT of possibilities for error there. How do the electronics make their computation?

hand calculated here.

problemchild
10-21-2011, 5:22 PM
You guys are using your car's onboard computer or electronics for your mileage numbers, I'm guessing...

I've always wondered how accurate those numbers are. I can imagine a LOT of possibilities for error there. How do the electronics make their computation?

Mine reads 1 higher than actual (hand calc)

stix213
10-21-2011, 5:36 PM
My 93 vette gets better gas mileage at 65 than 55, but I'm sure that's because at 55 I'm only in 5th gear, but at 65 I'm in 6th gear and actually running at a lower RPM. I just found that interesting when I discovered that.

Scout2Diesel
10-21-2011, 7:50 PM
I read up on hyper mileage tricks a while back. Got the Honda to increase from 25 to 31 mpg for the full tank average.

Really gets LA people when you do < 55 mph.

xrMike
10-24-2011, 10:15 AM
hand calculated here.

Mine reads 1 higher than actual (hand calc)

Yeah, seems like the only way to REALLY know for sure is figure it out the old-fashioned way (start with a full tank, drive it "x" miles, fill the tank again, check the # of gallons used, check the mileage travelled on your trip meter, and do the math).

I remember reading something awhile back about how a particular car's electronics calculated its MPG, and they explained it was based on some kind of vacuum reading. It "estimated" the actual mileage based on a vacuum reading somewhere in the fuel system. I remember thinking that the only way to know FOR SURE the accuracy of that estimate would be to double-check it manually, like you did PC...

I'm guessing a general rule of thumb for finding the best mileage in any vehicle would be to go whatever speed gets you up into the vehicle's top gear, and then keep it at the lowest RPM in that gear (without lugging the motor).

Wind resistance is the MPG-killer, if I remember correctly. Doubling your speed causes your drag to qadruple. Or something like that.

shooterfpga
10-24-2011, 10:19 AM
yeah wind is not a friend when you have dumbo ears for front fenders.

Maddog5150
10-24-2011, 10:35 AM
You guys are using your car's onboard computer or electronics for your mileage numbers, I'm guessing...

I've always wondered how accurate those numbers are. I can imagine a LOT of possibilities for error there. How do the electronics make their computation?

Its actually very easy with OBDII. With the computer being able to both regulate the amount of fuel usage as it tries to get as close as 14.7 to 1, the RPMs, MPH, consumption rate, barometric pressure, altitude and the list goes on and on, the cars on board computer will be able to figure out the numbers better than any human ever could. Think of someone trying to solve complex trig problems using acabus as opposed to a program on a modern day laptop that with a program designed for it

Darklyte27
10-24-2011, 4:47 PM
Got a Honda Fit for better mpg cargo capabilities, better than my 4 banger camry on mpg. camry has longer range at 18 gal tank and the fit is 10.8
half my commute is freeway, other is local streets. I drive about 150-175 miles a week and fill up 5 gallons.
Speeds on freeway is about 65, local streets about 35-45.
It comes out to around 30mpg.

On a camping trip where we were on the freeway for about 160 miles i got around 36 mpg because i was taking our time to get there, not in a hurry and drove about 60mph.

We also had about 250-300 lbs of gear, tent, clothes, stove, propane, food, water, my ham radio, antenna, batteries etc.
wife and I combined about 270 lbs

so when you bug out, you will probably not always drive at that speed. people trying to hop on your car for a ride? run away from zombies, weight in your car, water, food, dog? other people?

SoCalJ
10-24-2011, 7:41 PM
You guys are using your car's onboard computer or electronics for your mileage numbers, I'm guessing...

How do the electronics make their computation?

On newer cars the instantaneous MPG is calculated by how long the injector "pulse" is and the reading is very accurate...

mag360
10-24-2011, 7:48 PM
in my jeep I get best mileage at about 45mph. Well over 20mpg. I can do 21mpg at 55mph. It goes to only 19 at 70mph, 14 at 90mph.

thai562
10-24-2011, 8:10 PM
Most car get the best MPG at 55mpg. but its depend on the car drag coefficient. The more aerodynamic the car is, the faster it can go to be most efficient.
My 95 integra get 30mpg at 60mph, but I have to drive like an old lady.

thai562
10-24-2011, 8:10 PM
Most car get the best MPG at 55mpg. but its depend on the car drag coefficient. The more aerodynamic the car is, the faster it can go to be most efficient.
My 95 integra get 30mpg at 60mph, but I have to drive like an old lady.

nicki
10-25-2011, 4:07 AM
Took my 95 TA for cruise this weekend from San Jose to Fresno.

Going to and from I averaged 18.9 mpg hwy. Of course the drive was not flat run and I had some slow spots to drive through.

Since my car is a T Top, I had the roof off and I know that cost me probably at least 2 mpg. My cruise speed averaged between 70 to 75mph.

I notice when I drive with the roof on my car's operating temperature drops a few degrees.

My car seems to like to run between 2200 (80mph)and 2500 rpms(91mph), so until I move to either Texas or Utah (80mph speed limits), I won't be able to take advantage of what should be better fuel economy.

Driving at slower speeds drops my gas mileage since I have to down shift to lower gears.

Now my car is heavily modified, it has a 383 stroker. If it runs without problems, I will get it dyno tuned in the spring which should help increase fuel economy by at least 15 percent.

Right now the car is running rich and the tuning could be advanced a few degrees.

For all of you guys who drive SUVs or Trucks, you vehicles unfortunately have bad aerodynamics so you probably will get best fuel economy at turtle speeds.

Nicki

drunktank
10-25-2011, 10:00 PM
Good info. On my new scion TC with auto tranny I average 35mpg plus if I cruise around 50mph and use cruise control. Sticker says 31mpg hwy. This is the only vehicle I've owned that could surpass what the sticker claimed

Scout2Diesel
10-25-2011, 11:12 PM
After reading/trying out the Hypermile info.... it occured to me that lower rpms gives the combustion mixture more time to burn. Hence a more efficent engine and less heat wasted out the tail pipe.

My Ram 2500 CTD gets 18+ mpg ( 600 mile trip avg 80mph). I think the diesel has a huge advantage as the fuel mixture can vary between 20 & 40 to 1.

I think you would be suprised how far you can go on your fuel if it was "all you had". Some of the tricks are just smart. Others like coasting with the engine off are not the best for your autotrans, but if you needed to....