Better Mileage Shifting Manually

[AzNMpower32]

Originally Posted by mwares212

By the way, almost 6 months and ONLY 2,000 miles. You have to get out more.

Last time I checked, my friend had only put like, 1600mi after 6 months. His parents barely drive it to work due to the fuel consumption. 12 miles to the gallon in the city is not funny.

[y5choi]

it's worse in the winter months due to allegedly added antifreeze type additives in gasoline during winter time also with heated seats, defrosting AC compressor etc...

Anyway, I;m happy with the 4.8i especially doing highway. i can almost get it to go 700 km. Almost 28 imperial MPG

[Texas5]

Originally Posted by M3Armand

...if I drive my 4.8i X5 in "D", I get a little over 18 mpg in complete highway driving. If I shift myself, I get 20-21 mpg. Admittedly, I shift BEFORE it gets to 2000 rpms. Yes, it somewhat defeats the purpose of getting the V8, but I am liking the fact that I am actually "beating" the advertized mpg. I usually drive 75-80mph on the highway.

Maybe I'm missing something, but how does manually shifting affect your highway mileage? Speed would be the bigger factor, as you should be in top gear all the time (assuming it's not a very hilly area).

FWIW, I get 15-16 in mixed/mostly city driving and 18 (80+mph) - 21 (~65mph) on the highway. Pretty much EPA numbers.

Vehicle now has 8,500 miles on odometer.

[Mabuhay]

Originally Posted by Texas5

Maybe I'm missing something, but how does manually shifting affect your highway mileage? Speed would be the bigger factor, as you should be in top gear all the time (assuming it's not a very hilly area).

FWIW, I get 15-16 in mixed/mostly city driving and 18 (80+mph) - 21 (~65mph) on the highway. Pretty much EPA numbers.

Vehicle now has 8,500 miles on odometer.

While on the highway, the car downshifts while you are passing. When you get to a toll booth, you do some stop and go's. I was surprised to see how much this mattered. When you go on slight uphills, it also downshifts. When you shift yourself, you have control over whether or not you want to downshift out of 6th gear.

No, technically speed is NOT the biggest factor in determining mpg while "cruising" on a flat highway. It's drag coefficient and weight. It's RPM (i.e. - how fast your engine is spinning, and therefore, consuming gas) and any acceleration. If you keep both on the low end; i.e. - slow acceleration while keeping RPM's low, you would get the best mileage.

[Texas5]

Originally Posted by M3Armand

While on the highway, the car downshifts while you are passing. When you get to a toll booth, you do some stop and go's. I was surprised to see how much this mattered. When you go on slight uphills, it also downshifts. When you shift yourself, you have control over whether or not you want to downshift out of 6th gear.

No, technically speed is NOT the biggest factor in determining mpg while "cruising" on a flat highway. It's drag coefficient and weight. It's RPM (i.e. - how fast your engine is spinning, and therefore, consuming gas) and any acceleration. If you keep both on the low end; i.e. - slow acceleration while keeping RPM's low, you would get the best mileage.

OK, I thought when you said "highway" you meant relatively flat Intertate w/o significant traffic, and no toll booths etc. that required you to stop.

As to your second point, since the other factors you mention (drag coefficient, weight) are basically fixed, then speed IS the one variable that makes a difference in mileage. (you also mention RPMs, but it should be a given that you're not cruising highway speeds in less than top gear) In fact, aerodynamic drag increases at a rate equal to the square of velocity (i.e. a 20% increase in speed means a 44% increase in drag). So speed is a mileage killer......unless you're on the moon.

[Mabuhay]

Originally Posted by Texas5

OK, I thought when you said "highway" you meant relatively flat Intertate w/o significant traffic, and no toll booths etc. that required you to stop.

As to your second point, since the other factors you mention (drag coefficient, weight) are basically fixed, then speed IS the one variable that makes a difference in mileage. (you also mention RPMs, but it should be a given that you're not cruising highway speeds in less than top gear) In fact, aerodynamic drag increases at a rate equal to the square of velocity (i.e. a 20% increase in speed means a 44% increase in drag). So speed is a mileage killer......unless you're on the moon.

Ok, so I guess we will be "geeking out" here. With drag coeff being constant, if you're travelling at 70 mph and driving the engine at 2000 rpms (roughly) at 5th gear OR you're travelling at 70 mph at 1500 rpms (or so) at 6th gear, at which gear would you be burning more gas? Answer is 5th gear since the rpm is higher. It has nothing to do with the speed.

[Texas5]

Originally Posted by M3Armand

Ok, so I guess we will be "geeking out" here. With drag coeff being constant, if you're travelling at 70 mph and driving the engine at 2000 rpms (roughly) at 5th gear OR you're travelling at 70 mph at 1500 rpms (or so) at 6th gear, at which gear would you be burning more gas? Answer is 5th gear since the rpm is higher. It has nothing to do with the speed.

Well, Armand, I guess you're right. Yes, if one is stupid enough to purposely drive around at 70mph in 5th gear, he'll get worse mileage than if he drove in 6th gear.

Someone call CNN and inform them of Armand's scientific breakthrough!!!

Hey, I just thought of another one: Driving w/o the parking brake engaged improves highway mileage (speed being constant, of course).

Energy crisis - SOLVED!

(just kidding with you, man!)

[Bigtop]

It also downshifts if you are going down a long hill or grade on an interstate. I use manual in this case to keep it in 6th.