I was reading something pretty extensively tested and thorough a long time ago on the internet. I think it might have been at howstuffworks.com That's one of my favorite sites to visit about automotive stuff, because I don't know much yet. Anyways... they had done extensive testing to find out what the best possible speed is to get the best mileage for your gas... and the winner is...

65 MPH.

The absolute best speed you can possibly go to get the most gas mileage is estimated around 65 MPH. It's not a government ploy to get you to stop speeding, it's simple physics. The amount of gas it takes to speed is factored into the distance you'd be going at that speed and the peak of distance per speed is reached at 65 MPH.

Any faster than 65 MPH and you're using too much gas for negligble distance gains, and any slower than 65 MPH and you're not gaining enough distance for the amount of gas that it takes to get there.

This is just a little FYI - If you're on a long trip somewhere and you're as strapped for cash as I am (I have 3 dollars) DONT FORGET - 65 MPH is your friend. I know that's practically blasphemous in a Cobalt (I never go 65 - lol) but it really does work.

You can test it by looking at your estimated MPG while staying at 65 for a long time.
-Aleckor

 

depends on the car and on the gearing aswell.. but 65mph could be a good median number to start with

 

In the automatic 2.2, its 45-50 mph

 

I was under the impression it was 55.

 

It seemed like 80-85mph in fifth was netting me 32-33 mpg.

 

Trust me, reset your mileage meter, find some level ground, and set your car on cruise at like 47mph, and watch your MPG match it

 

Yea, Every car has to be differant but I bet 65 is a great spot. I get best around 60 I think.

 

aerodynamics plays the biggest role in mpg and what speeds will yield the highest ratio

 

70mph with the windows and sunroof closed FTW

 

It's usually around 65 on most cars. It depends on a number of factors tho.

If you look close enough, you'll find that even the temperature of the air affects gas consumption.

 

Right, of course it depends on your specific car and a bunch of other factors... but what I meant was that 65 is the estimated "sweet spot" on every single car. It's just estimated. Of course it'll be different for each individual car.

But next time you're on a long trip, 65 is a good place to start testing your MPG. It'll save you thousands of dollars in the long run.
-Aleckor

 

I get my best mileage (about 35 mpg) around 60-62 mph in my Cobalt.
I get my best mileage (about 12.5 mpg) around 40 mph in my lifted Jeep Wrangler... Go figure

 

Hmm, I've found it's the rpms, about 2750 in 5th gear on the hiway seem to be where I'll peak at. Any faster and the estamated mpg begins to drop.

 

I also agree completly, with an auto, the torque converter locks up and engine barly works to keep the car moving.

 

you cant really set a certain number like 65MPH, becasue people will disagree with it no matter what. For me, i have found 105KM/H is the sweet spot. ( i dont know what that is in MPH)

 

the biggest factor is wind resistance. right around 55 mph is when the wind resistance starts to play a huge role in your gas mileage. after that it comes down to gearing.

 

That's 65mph. Also the sweet spot for me. Was getting 45 mpg at that speed following a semi.

 

lol now im a hypocrite

 

I find the best mileage for me is around 75Km/h. Drove home in a snow storm and instead of doing 100-110, i did 70-75 and got close to 40MPH.

 

i noticed that in the morning on the way to work.. if i set the cruise at 65 MPH.. i get good MPG.. but if i set it at lets say 75-80 mph i get a lower MPG.

later

 

I think its closer to 50mph from my experience.

 

Exactly what I am getting...

 

The lower you are in the rpms on the highway,the better gas mileage you will get.You cant go by speed.If you doing 60 mph in 4th gear and 60 mph in 5th gear,your gonna get better mileage in 5th because your running at a lower rpm.

 

Actually the best speed is much lower. Normally around 30 mph. Not that this info is useful; who's gonna drive that slow? In general slower means less air resistance but you need to be in high gear.

 

Close to being true, but not quite. Gas consumption is directly related to the amount of throttle you use. If you're going up a steep grade at 60 mph in 4th gear and moderate skinny petal you will get better gas mileage if you're going up a steep grade at 60 mph in 5th gear but have to put the hammer down in order to have the power you need to keep speed.

I know this from a stint in Nebraska during a roadtrip in my Wrangler before I got new gear ratios... There were 50+ mph sustained headwinds. I spent a lot of time in 5th gear trying to keep speed and got an aweful 8 mpg. I'd shift into 4th (and use less throttle to keep speed) and I was getting upwards of 10-11 mpg. Still horribly low, but better than 8 mpg...

Yep, it's why the Corvette Z06 got such good gas mileage in the city. They did the test at those low speeds in 6th gear! If you're chugging along nearly stalling the engine at 30 mph you're gonna get some pretty nice mpg numbers