Can you get 30+ MPG going 70-75mph?

[sikest]

I get 32.8 as shown on the computer on my day to day commute which is 20% city and 80% highway @70mph. The actual MPG at fill up is really 30.1-31.1.

For road trips we have gotten as low as 32.5MPG and as high as 40MPG with an insane tail wind. I am at 15K right now and have noticed that the MPG is improving as the car breaks in.

[00NissanNinja]

Originally Posted by carbonBLUE

that isn't bad considering the elevation changes

MT or AT?

A manual, overall its downhill after passing through just a bit of Kansas heading east. There were lots of hills though for sure. The funny part is the elevation actually goes up a bit more from Denver heading into Limon CO. Once I got closer to Ohio it was more like 31.5 mpg (But I did throw a bit of fun in there once I broke it in). The car was also fully loaded. Four tires, baggage for two, stuff I was bringing to my place in OH, etc.

[carbonBLUE]

Originally Posted by 00NissanNinja

A manual, overall its downhill after passing through just a bit of Kansas heading east. There were lots of hills though for sure. The funny part is the elevation actually goes up a bit more from Denver heading into Limon CO. Once I got closer to Ohio it was more like 31.5 mpg (But I did throw a bit of fun in there once I broke it in). The car was also fully loaded. Four tires, baggage for two, stuff I was bringing to my place in OH, etc.

yeah its hard for me to go on long trips without opening the car up once or twice lol :P and every time i pass a dirt road that looks like it goes off to no where it doesnt help either because dirt roads + rwd is heaven

[Dadhawk]

Not too long after getting the FR-S I took a road trip where I knew I was able to fill-up, hit the highway, and calculate my average speed based on mileage and time. These were the results (documented here, along with what happens when you use the FR-S as a soapbox derby car):

08/14/2012: 270.50 Miles, 33.08MPG Highway Calculated Avg Speed 72.4 MPH
08/16/2012: 276.50 Miles, 31.60MPG Highway Calculated Avg Speed 73.2 MPH


I later took a similar trip on a different (less elevation change) road and got this, although I didn't calculate the average speed as precisely. This trip (documented here) included 45 minutes of bumper to bumper traffic as well:

12/14/2012: 395.20 Miles, 35.60MPG Highway Speeds (70+MPH)

[Dake]

Originally Posted by chrisl

Technically, no, it isn't. Exponential means that it is of the form k^x, where k is some constant. Quadratic is a special case of polynomial, which is of the form k0 + k1*x + k2*x^2+k3*x^3+...+kn*x^n (where k0, k1, k2... are constants). Exponentials grow much faster than polynomials (in the limit as x --> inf), which is why I said quadratic drag is quite a bit better than if it were to increase exponentially.

http://www.knewance.com/comparisons/...ic-growth.html
http://www.math.ucla.edu/~bnelson6/E...ial_Growth.pdf

(and as I said before, I know I'm being pedantic, but I can't help it on technical topics, since I'm an engineer...)

It's generally accepted that drag increases with the square of the speed. For the purposes of the discussion, the result is the same: lots more gas to go a little faster.

[Nefded]

On average, with mixed driving I'm getting ~31mpg manually calculated. I cruise at 80-85 on the highway too

[chrisl]

Originally Posted by Dake

It's generally accepted that drag increases with the square of the speed. For the purposes of the discussion, the result is the same: lots more gas to go a little faster.

Yes it does - and drag being proportional to the square of the speed means that it is quadratic, not exponential. That's what I was getting at there. Also, with cars, you have to balance a number of additional factors - rolling resistance is approximately constant at all speeds for example. This means that the total resistance acting against a car's motion is nearly constant at low speeds, and starts to increase dramatically at high speeds (which is why crawling along at 15mph isn't necessarily the best for gas mileage). You also have to balance all of this against the engine's efficiency curve - lugging the engine at 30mph might cause you to get worse gas mileage than cruising along at 55mph at 2500rpm for example. Nearly all modern cars do exhibit a sharp falloff in efficiency above 70mph or so, though, simply because they're designed with that kind of cruising speed in mind, and as such, the aerodynamics, rolling resistance, engine efficiency curve, and gearing is designed around cruising efficiently at 50-65mph.

(as I said in the last post, sorry about the pedantry, but I'm an engineer with a masters degree in fluid dynamics, so I tend to be picky about these kinds of subjects)

[Karl07]

I don't know if your fuel is worse or what over there, but here I have managed to average about 44mpg (5.3L/100km).
I thought it was 5.7 but I found my paperwork from my experiment.
2012 6AT GTS, stock condition.

Now that I have modified my car, I am only getting 34.9mpg with 18x9.5 wheels.

But driving like that is boring.

[Celadrielas]

I live in AZ... I am currently driving at 28.1 city on avg when I burnt a full tank on just hwy driving I was at 34.6 mpg. Avg speed was cruise control set at 75

[White64Goat]

Drove to Virginia Beach 2 weeks ago and got 31.69 mpg and probably ran around 70 most of the way.

[FRSure]

Im still break in period about 700 miles.. I get 28mpg highway... Automatic.. Is that normal? :\
Driving 80/20 Highway/City

[dnieves]

Speaking of the trip computer, how accurate is that thing? When I use average it seems pegged at 25mpg even with I granny drive or try to hypermile..

[spyingwind]

I can get the mpg up in the 40's if I stick it in 6th and cruise at about 45mph.

[Turbowned]

My overall average right now is 27mpg combined with my commute being about 50% highway, 50% backroads and frequent start/stop conditions. I'll take it considering my Audi gets 15mpg doing the same commute (granted it weighs 1,200lbs more and makes 2.5x the horsepower and torque)