Which MPH gives the best MPG ?
 

I tried setting the cruise control at 55mph, 60mph, 65mph, and 70mph while driving on the freeways....

Which one is going to offer the best mpg for my mph? Is it really the slower the better? My results were inconclusive....

If all of your testing parameters were the same, i.e. road driven, weather conditions, etc, and your results were inconclusive as to which speed provides the optimum MPG's, I say drive whatever speed you like given the road conditions will allow.

With the way things are going, I believe you may have the best answer!

Zero.

http://i851.photobucket.com/albums/a...asy-button.jpg

The correct answer, actually, but it really is the slower the better.

Just understand that aerodynamic drag increases a the square of speed, i.e. doubling your speed increases drag 4 times. Fuel burned is a function of work performed. Faster you go, you do more work to overcome drag and your engine turns faster in any event.

But go fast enough to stay in top gear!
 

With both our '06 E500 and my ancient '76 Porsche 912E (and even with my '91 F-150 with E4OD trans!) anytime we're much below 55, the engines want to be down a gear or two and that wastes a lot of gas, compared to a few kph faster.

Normally I would agree with the slower thing but these cars are designed with gearing and tuning for the Autobahn. During a roadtrip in my E550 running around 65mph the avg mpg was showing about 28, we hit a state where the speed went to 70 so I kicked it up to 80mph and the avg mpg started climbing, even though we were more than half way thru the tank, by the next fill up the avg had gone to over 30mpg. The next tank was all at 80mph or better and the avg mpg was 32.? for the tank. Not saying that you can run 110mph and get even better, I'm sure there is a point where it starts dropping again, but there has to be a sweet spot where these things get the best efficiency.

And what planet did you perform this test on?

I've never seen my 08 E550 show over 29mpg on a flat road with cruise control on.

To get 29mpg, I need to be doing around 60mph or so IIRC.

I've done some 120 mile trips all highway and seen 28mpg on the computer. The computer is off by around 1mpg compared to manual calculations at the pump. So the E550 can do 27mpg-28mpg .. not sure about driving 80mph and getting 30mpg .. maybe the computer shows that, but need to do manual calculations to back that up.

100 kph for an E90 BMW 320 with efficient dynamics yields the best result. Excursions to the Autobahn at speeds no lower than 150 cut my range in half. Drive like a maniac and the range is 1/3.

The best real world results are to be had when driving the speed limit (or close to it), and CARRY YOUR SPEED! Accelerate on downhills using the cruise control, lift early and brake late.

Vik, 120 mile trip is about 1/4 tank of gas your judging the whole tank on. My house is 20 miles from Interstate 95, once on that about 1200 miles later I'm in Miami, that gives me the oppurtunity to observe several tanks of gas at highway speeds getting there and back. Next trip I'll get pics of it and run the numbers at the pump also, but the mpg calcs in the car have never been off by more than +/- .1 so I quit checking it after a while.

I have found 3 factors that effect my mpg are 1. tire pressures. 2. fresh oil change. 3. clean air cleaner element. My best mpg's are when these items are optimal. Tire pressure being the biggie. Max in the front under the engine and 2 pounds under in the back unless you carry a lot of weight in the back. My tires also wear much longer and the car handles better.

Also is there any way to tell the instantaneous MPG figure as you are driving? I found this very useful on my Volvo but a bit perplexed why it is not there in my car... Would be a very useful figure to keep an eye on as I drive to see how different scenarios affects the mileage.

My 07 Chevy Tahoe has this feature. It is pretty cool when the engine switches from firing all 8 cylinders to only firing 4 and see instantaneous MPG's jump up over 40!!! Then reality kicks in as does all the cylinders and the instant MPG's drops to 15. No matter how conservative or agressive I drive, the average MPG's is always 15.9

well i'm always floating at 17.5 to 19.. sometimes 15.5.... and on the highways about 21 to 23. This is in Southern California driving though...

I try to stay in my top toque range , and in my diesel that is where I see the highest mileage.
It works for my Land Rover and its gas , but it gets such bad mileage 14 mpg or 14.5 mpg I just drive it the extra 1/2 mpg it just not worth the time.

Started with a full tank, did the trip, refueled to full and did my calcs that way.

In any event, I'm not saying your numbers are not valid. I'm just providing the numbers I've gotten to whoever didnt believe your claims because the 5.5L V8 w/ 7G in our cars puts out some impressive numbers.

Like someone wrote, it can depend on a lot of things .. better tires, properly inflated tires, better roads, weather, etc .. so maybe under certain conditions you can get 30 ..

Here is a factor that most do not consider:
Interstate driving (on our vehicle) produces about 5% better mileage at a higher average speed. Several times a year we travel from Atlanta to the Gulf coast. We can vary our route somewhat but of necessity, it includes two lane and interstate roads. Typical yield for two lane driving is about 28.5 mpg at 65 mph with air on of off ( I cannot discern any extra fuel for A-C although I know it must require some) Nothing I can do to get it to go higher. On the interstate ( gradual slopes, wider curves) we can average 75-78 mph and consistantly get 30 mpg plus. Same deal about A-C. Intuitively I believe that slower interstate speeds would yield higher averages but the cars readout does not bear it out. The sweet spot appears to be about 75 mph. I am certain that red light idling is the biggest factor in the better average . Kind of like getting a 0 on your test paper, really tough to bring up your average.

My mistake then. Your right, alot of things can affect it, I got in my Yukon Denali after my wife had taken our son to college with it and it showed 21mpg average, I never get more than 16 with it, still don't know how she did it. And that vehicle definately doesn't get better MPG going faster, in fact it drop significantly over 65mph......

I am amazed at the numbers I am seeing in this thread (28mpg .. 30mpg !!). I guess folks are reporting their all time best MPG like when doing a 1200 mile trip on I95. I am new MB driver (E350 4matic), the best I get is about 26mpg in medium length trips (~50miles) here in central NJ. During startup, before getting on the highway and when the engine is cold, I see numbers in 17 to 19 MPG range, but once I get on the highway, MPG picks up. Also, the best I have seen so far is 26.5 while doing 55MPH on a county highway. At 65MPH, I get between 25MPG and 26MPG. And I am a very cautious driver, accelerate slowly, look half a mile ahead and adjust speed accordingly (e.g. if the traffic light half a mile ahead is red, I will start to slow down, I am almost always in the right lane). I think these cars are rated for 17MPG city and 24MPG highway. So, 30MPG and 32MPG numbers at 80MPH are really great...too great!

An '08 E350 4-Matic is rated at 16/22 so your numbers are great also.....my '07 E550 4-Matic is rated at 13/19 and we've never gotten 19mpg out of it, not even with city driving, worst I've seen is 22mpg driving in the snow this winter. So those rated numbers are pretty much worthless as indicators.

And yes I did post my best over a 1200 trip (have done it 3 times in this car actually), the post was about what MPH gives the BEST MPG, not what do you get on a daily basis. Normally we see 24-26MPG in our normal country living small town driving days with some 30mph zones and stoplights and drivers that can't seem to manage one speed without a 20mph variance.....

Awesome insight guys!

I had my suspicions that the sweet spot was 70ish.....

Wow that is very impressive. In Washington DC driving, even being careful, I usually hover around 14-16 MPG on my E550. The good thing is I rarely have to push the engine so that probably keeps the MPGs from getting any worse because if I push the car, I run out of road very quickly :)

I think people need to post up pictures like this to justify some of the claims flying around this thread. In my E500 at 65-70 this is the best she will do; around 24 mpg.

http://i403.photobucket.com/albums/p...7/IMG_0154.jpg

Agreed some of these numbers are awfully high...?

Best I have ever seen in my 07 E550 is about 24-25 mpg. That was going about 90 Km (56 mph) with the spare on.

I usually get about 22.4 mpg on the highway and much lower around town. Espcially with the way I drive...:D