BetterMakeWay

Short question: Why do some think that using DS gives u better mpg than in D?
I mean, logic and the manual dictates the oposite...using DS will indeed start in the 1st gear, but it will have higher shift points, and it will select either XS or S mode wich either way you put it it will not give better mpg than E an XE.

EBMCS03

Cuz you get to your cruising speed faster and can then let off the gas pedal and feed the car less gas.

So say like in D you step half way down the gas pedel for 15 seconds before you reach cruising speed now you burned 15 seconds worth of half throttle gas.

and in DS you step on the gas at half throttle for 8 seconds and u reach cruising speed you only burned 8 secodns worth of gas at half throttle...


Over simplifying again but hehehe its somthing to that extent... there was a thread on it somewhere here...

cobradav

My own experience is what you would expect, better gas mileage in D than DS. If I use manual mode I might better D if I truely babied it, started in M3 for instance and shifted earlier than D does. Not worth the effort as I get excellent mileage for my driving style. At 17,900 miles and 1 year (61 tank fillups) I have averaged 20.9 calculated and 21.8 if I were to believe iDrive.

BetterMakeWay

I think it's not the same...after all in ds you will burn gas less (as in time as you say it) but in quantity more...after all the valves will open more as the engine reves higher. So imo that's not really a valid point.
I thought that if indeed it gives better mpg wich from my experience i can't say it does...it must be smth to do with selecting the 1st gear all the time, lurking too much in 2nd untill u get to change to 3rd might be a reason but i reallly don't know.

KiritPatel

One thing I don't understand: If I'm cruising at 80 mph on the motorway, in D mode the engine revs at 2500 rpm, in DS mode it revs at 3000 rpm. What happens to the extra energy since my speed is constant?

BetterMakeWay

In ds you might find yourself in a lower gear. The extra energy is spent in vane imo.

EBMCS03

Thats only for cars with the older software I think... I forget which version but since people have been reporting that even in DS mode the car will shift into 6th gear. What you're talking about with the 2500 and 3K rpms is cuz before in DS mode the car will not shift into 6th.

KiritPatel

Sorry, should have said, this is in my E39, will try in next week in my E60 and let you know.

cobradav

I think your under the impression that time has something to do with MILES PER GALLON. That is not the case. Just like you would not speed up if u had 1 gallon left in your tank to get to a gas station quicker, accelerating to a speed quicker and then maintaining that speed is not the way to get better MPG. Hitting the sweet spot (and staying constant) is the trick. Taking longer is of no consequence if u get better mileage. There is a happy medium where the engine is most efficient in distance versus gas used. It is not the lowest possible RPM nor is it the highest. If one had the time you could do you own test of travelling a set distance of say 10 miles at constant RPM and see how much gas was used at 500 RPM increments starting at something over 1000 RPM. I have done this in other cars that have computers indicating MPG, Avg MPG and actual gals used, measured in 0.1 increments. Using these same tools u can see the effects of rapid versus slow acceleration and I can say that slow and steady wins the MPG race on the vehicles I have driven.

EBMCS03

Ya I know. it was a quick answer to how it is possible to get better mpg while using DS w/out getting into all that detail.