Speed vs Fuel Efficiency

[dm]

At around 172 mph I get 14.4 mpg,
At 160 mph I get 16.1 mpg.

At 185 I only get I'm down to around 13 mpg and rarly go that fast. That's just to high a fuel burn to make much difference in the length of my trips.

This is at around 5000 feet and this is with no wind.

I generally cruise around 160 to 165, around 15 mpg.

My wife drives a hybrid and gets around 40 mpg to balance things out.

 

[ExFlyBoy5]

At around 172 mph I get 14.4 mpg,
At 160 mph I get 16.1 mpg.

At 185 I only get I'm down to around 13 mpg and rarly go that fast. That's just to high a fuel burn to make much difference in the length of my trips.

This is at around 5000 feet and this is with no wind.

I generally cruise around 160 to 165, around 15 mpg.

My wife drives a hybrid and gets around 40 mpg to balance things out.

Although I haven't bought avgas in quite a while, I'm going to guess you are spending $5~6 per gallon.

Sent from my mobile device so please excuse grammatical errors.

 

[dm]

Although I haven't bought avgas in quite a while, I'm going to guess you are spending $5~6 per gallon.

Sent from my mobile device so please excuse grammatical errors.

It a little under $5 for 100ll at the SS pump. Ethanol free is $4.40 .

 

[braumeister]

Temperature doesn't seem to be the factor

That surprises me, because in my experience it's a big factor. I always get much better MPG numbers in summer compared to winter.

 

[Midpack]

Temperature doesn't seem to be the factor

That surprises me, because in my experience it's a big factor. I always get much better MPG numbers in summer compared to winter.

We've always gotten lower MPG in winter, and it's more pronounced now that we have two hybrids. On tankfuls, I average as much as 56 MPG in summer, and as low as 44 MPG in winter. DW averages about 41 MPG in summer, and about 34 MPG in winter. When we have a long stretch of single digit temps in winter, it's really obvious, MPG and range!

Cold weather and winter driving conditions can reduce your fuel economy significantly.

Fuel economy tests show that, in short-trip city driving, a conventional gasoline car's gas mileage is about 12% lower at 20°F than it would be at 77°F. It can drop as much as 22% for very short trips (3 to 4 miles).

The effect on hybrids is worse. Their fuel economy can drop about 31% to 34% under these conditions.

Fuel Economy in Cold Weather

 

[Closet_Gamer]

Honestly this is an area I don't worry about much. I buy cars that get decent mileage but are still fun. I take the train to work so my driving commute is typically about 3 miles. I save ~$500/mo by taking the train vs. driving.

LBYM in a huge way overall and just budget gas money each year.

When I do take a road trip, not worrying about how fast I drive and the associated impact on MPG is one my little LBYM rewards.

 

[Sunset]

On long trips I drive 5->9 miles over the speed limit, as long as someone passes me.
I don't want to be the fastest car on the road as I don't use a radar detector.
Personally I value my time more than the $25 I might save driving at 55.
After all I can always make more $$$, but I cannot make more lifetime.

I always use cruise control, once you do that you see who is not using it, they pass me, then drift back then pass me again and repeat.
Last trip of 800 miles, I checked the mileage and at generally 75 mph I got 34 mpg in an old toyota Camry that has a 4 cylinder engine. Tires were at 33lbs, used AC and windows were closed all the time.

 

[mpeirce]

> Tires were at 33lbs

I've noticed that in our old Nissan Murano tire inflation made more of a difference to the highway mileage than the speed on the highway (within reason of course).

It pays to have tires inflated to the maximum PSI.

 

[calmloki]

We've always gotten lower MPG in winter, and it's more pronounced now that we have two hybrids. On tankfuls, I average as much as 56 MPG in summer, and as low as 44 MPG in winter. DW averages about 41 MPG in summer, and about 34 MPG in winter. When we have a long stretch of single digit temps in winter, it's really obvious, MPG and range!
Fuel Economy in Cold Weather

Poor expression on my part. My fuel economy is worse in the cold. I was speaking to driving at altitude, and was trying to say that I was comparing similar temperatures at high altitude and low as well as comparable average speeds at high and low altitudes. I am puzzled by the measured superior fuel economy my car gets at high altitude. Air resistance? If I could keep my foot out of it perhaps it would return better numbers at low altitude as well, through a reduction in air resistance. Maybe the engine computer is doing just fine compensating for the higher oxygen density at different altitudes and temperatures and it is all air resistance.

I still dislike ethanol, which is often added in winter, but that is a digression.

 

[gozer]

That surprises me, because in my experience it's a big factor. I always get much better MPG numbers in summer compared to winter.

It could be the geographical differences in winter. Cars do often work a bit better in 'slightly' lower temps. At the track we had to adjust our 1/4 mile handicap times after the sun went down because the car would run about .1 seconds faster in the cooler air. (65 degrees vs 75 degrees) So perhaps if someone lives in the south and has a 'faux winter', maybe it doesn't get cold enough to hurt much.

I live in Ohio. It gets cold enough here in winter that it hurts my gas mileage noticeably.

 

[ls99]

Just had an appropriate air density v speed test. Returning from the mancave last night, a section of a long downhill from 2750 feet to around 1300. Typically my pickup truck gets well past 75 in third gear foot off the gas pedal in temperatures of 65 to 80F.

The ambient temp was 37F at the top of the hill, and 43F at the house at 7 PM.

The truck attained max 67 MPH. Same body configuration, open bed, closed wndows, dirty as usual, tire pressure at 55 PSI, etc.. I typically brake around 65 and get it down to 55 several times, unless...... I am testing.

Edit add: This test excluded anything the engine does, strictly gravity, air density and speed. Was not a test for MPG.

 

[Midpack]

All else being equal (except *), we get our best fuel efficiency when it's moderate-warm outside (about 70°F±), like late Spring and early Fall. MPG falls when it gets really hot, but I am sure that's because AC * kicks in more and more. And as noted earlier, MPG falls off a cliff in winter, the lower the ambient air temps, the worse our fuel efficiency gets.

 

[ERD50]

Lotsa variables.

I'm pretty sure that an ICE is more efficient with colder air. Colder air is more dense, and therefore contains more oxygen. Engine like.

But in cold temperatures, an engine is harder to turn over, and takes longer to warm up and is less efficient until it is at normal operating temperatures. Plus tires have increased rolling resistance when cold (the rubber is stiffer), tire pressure will be lower, further increasing rolling resistance. All the lubricants are stiffer. The alternator has to make up the increased battery drain from harder starts. You might even be slipping and pushing through snow.

And... fuel mixtures change seasonally, and as mentioned, AC in summer versus heating.

My guess is that with extended highway driving, cold weather will give marginally better mpg. But the starts/stops that most of experience will mean lower overall mpg in winter.

-ERD50

 

[ERhoosier]

I don't drive much in wide-open spaces out West, but here in my region (Midwest) one can rarely drive a CONSISTENT 75+mph anymore. There are always clusters of vehicles driving slower, so real-world mpg penalty of trying to drive that fast is greater (from repeated accelerations vs steady speed) and real-world benefit is less.
On same highway trip between 2 big Midwest cities I've noticed no big net time savings trying to drive much over posted speed limits. The same cars you just passed a few miles back catch right up to you again as you reach the next rolling traffic jam (like big trucks matching speeds in both lanes ). So these days I just set the cruise at the posted speed limit & save (most) of the aggravation of fighting the slower traffic- and watching for speed traps.
BTW- on some length trips the better mpg's of driving slower & smoother can actually SAVE net time. On one of my mid-length (~350mi) routes I can drive ~65mph ave & easily make it straight through on one tank. Trying to drive 75+ knocks down the mpg's by ~20%(+) and forces a pit stop for gas. As any NASCAR fan knows, sometimes conserving fuel to avoid another pit stop can win you the checkered flag