Optimum mpg

[Dragon]

What the optimum mph should I drive to get the optimum mpg in my 1997 W202 and 2001 W170? Is it 55mph or 65mph? There are no trip computers in either.

 

[A210AMG]

I guess if you could 30mph would be best....


However when makers give 'best' mpg figures it generally at 56mph


Saying that what you get and what they say can be very optimistic..

 

[television]

What the optimum mph should I drive to get the optimum mpg in my 1997 W202 and 2001 W170? Is it 55mph or 65mph? There are no trip computers in either.

I would have said 55-60 just when the box has dropped into top,, this goes for most cars I believe. My V70R will do 35mpg at 55mph at 70 it does 23 ish

 

[Gucci]

Yes, don't use brakes, don't stop, drive on perfectly level glass surface continually and you might get the optimum set by manufacturers

 

[Bobby Dazzler]

There's a trade off between efficiency of the engine (influenced by engine speed) and aerodynamic drag.

The sweet spot will be different for each vehicle, but just like many old wives tales, 56mph is what many people think is the most efficient speed, and is probably about right.

 

[timskemp]

56mph (90kmh) and 75mph (130kmh) used to be tuned by manufacturers to be economical to fiddle the old fuel tests, however the reality in most cars is the lowest comfortable (say 1200-1500rpm) speed in top gear will be the best trade off between mechanical efficiency and aerodynamic drag.

As others have said though, braking is your enemy (there's a prius discussion elsewhere...) as that turns the motion you've used your expensive fuel to generate into heat - so you might as well just burn the fuel!

 

[BTB 500]

What the optimum mph should I drive to get the optimum mpg in my 1997 W202 and 2001 W170? Is it 55mph or 65mph? There are no trip computers in either.

Technically, you should engage 1st gear and drive at low rpm to get the best fuel consumption. But that's not very practical, which is why events like the Shell "mileage marathon" impose a minimum average speed.

So the answer to your question is to cruise as slowly as possible in top gear. 55 will certainly be better than 65.

Turn off the aircon too

 

[Roger Jones]

Apart from optimum cruising speed, smooth driving is key to good mpg, as mentioned above. Drive so that braking is minimized and you will be safer -- keeping good gaps around you -- and better off in the pocket.

Also, all the authoritative opinions I've seen say get up to your cruising speed briskly -- not fiercely, but briskly. And if you have cruise control then use it, but not in hilly areas. I reckon that using cruise control to get you up to cruising speed is good confirmation of what "briskly" is. Cruise-control systems are far more efficient than your right foot (well, my right foot anyway); there's a graph online somewhere showing curves for cruise control and right foot against an optimum engine performance curve -- the CC curve is much closer to the optimum curve.

Here's a bunch of good tips:

http://tinyurl.com/jtd4a

 

[television]

Reading all the tips from yesteryear always said,"get the car into Top as soon as possible" where cars have electronic braking systems and cruise or Distronic the optimum figure will not be got by using these systems as they use the brakes to slow the car, and often change to a lower gear on an incline.

The best figure should be obtained while keep a good gap in front, getting a run at a hill and some for sight as to what is going on ahead

 

[glojo]

Nothing will improve the mpg more than good driving. Good forward observation, good anticipation and of course always being in the right gear for the right speed.

I would suggest that every car will be different but never be in too high a gear, but don't be afraid to use the highest gear that is suitable for the conditions.

For a competant driver I would suggest that forward observation, coupled with anticipation will make the biggest saving.

John

 

[television]

Nothing will improve the mpg more than good driving. Good forward observation, good anticipation and of course always being in the right gear for the right speed.

I would suggest that every car will be different but never be in too high a gear, but don't be afraid to use the highest gear that is suitable for the conditions.

For a competent driver I would suggest that forward observation, coupled with anticipation will make the biggest saving.

John

As most cars are automatic it will always be in the right gear for the best part, this is where the 55 mph drops into the equation, the car will be in top

 

[Stratman]

Think about what actually happens when you are driving. If you are doing say 55mph and want to go slower do you increase or decrease the throttle opening?

You decrease it, burning a smaller charge of fuel at each combustion cycle. The engine, provided the car is in the same gear as before, is still doing the same number of revolutions per mile but each 'bang' happens with less fuel being burnt.
The opposite is of course true when you put your foot down to increase speed. Again, the engine is still turning the same number of turns per mile but each revolution consumes more fuel because of the larger throttle opening.

 

[glojo]

As most cars are automatic it will always be in the right gear for the best part, this is where the 55 mph drops into the equation, the car will be in top

Driving an automatic will indeed probably eliminate the need to change gear but what would be the sense in accelerating to a given speed when within yards there will be a need to slow down? All a driver will do is waste fuel and my point is that to give a mandatory correct speed will never be as black and white as we might like. In an automatic it would be crtazy to go down a very long hill on a motorway and periodically brake to keep to this so called optimum speed, again my point is all about forward observation. The driver can lift their foot off the throttle and let the car dfo its own thing. I have gone down Telegraph Hill which is a dual carriageway at 70mph (ish) and the computer was registering 99.9mpg. Should I have braked to rteduce speed?

I just feel that mandatory speed limits are wrong when answering such a complex question.

John

 

[television]

I just feel that mandatory speed limits are wrong when answering such a complex question.

John

What is this thread about, driving like an idiot of getting the most out of your car on a reasonable journey.

Purely on the basis that using the throttle uses fuel, and the further you press it the more you will use, its easy to work out.

Yes by weighing up the situation ahead is number one on the list. to quote roads near you the approach ring roads around Exeter are a good example where there are traffic lights, for me when there is a red light ½ mile down the road I am always coasting at this point, cars wizz past me, sure, but 4 sets of lights down the line I have not accelerated or touched the brakes, and I am behind the car that wizzed by me at the first set of lights.

On long slow descents the auto box drops into the engine braking mode, only after the car speed has dropped considerablly.

There are basic rules for every thing, on this matter they are

Get the car into top as soon as possible.
Avoid excessive braking and acceleration.
All cars have a best MPG around 55 to 60 mph, and that is to do with the gearing, and turbos where fitted cutting in, and this bit was the original question.

On the point of using the brakes, I never use mine if I can avoid it as it makes the wheels dirty

 

[IanA2]

On the point of using the brakes, I never use mine if I can avoid it as it makes the wheels dirty

 

[Bobby Dazzler]

With superchargers (kompressors) being common on MBs, driving off boost will also boost economy. By that I mean keeping revs below the point at which the clutch engages the kompressor, which for a C32 means keeping below 2700rpm, or ideally less than 2500rpm.

 

[television]

With superchargers (kompressors) being common on MBs, driving off boost will also boost economy. By that I mean keeping revs below the point at which the clutch engages the kompressor, which for a C32 means keeping below 2700rpm, or ideally less than 2500rpm.

So that would mean around 60 in top

 

[Dragon]

As most cars are automatic it will always be in the right gear for the best part, this is where the 55 mph drops into the equation, the car will be in top

When I first drove the W211 E200 Kompressor automatic earlier this year, I said to myself the auto has improved vastly since our 1992 W201 190E 1.8 four gear auto. When I pressed the accelerator there is no lag and I am amazed it changed to the right gears to pick up momentum. With the trip computer on it makes me very conscious it doing only 17mpg urban knowing very well the climate control is on that why the lower mpg.

 

[Dragon]

With my SLK roof down, I drove to and from London over the weekends around 60mph and cars keep overtaking me at 80mph or more. If I will to drive at 55mph I will be the slowest car on A12. 65mph seemed the optimum speed in relationship to other drivers. Nobody ever drive at 55mph unless it a very old vans or vehicles without MOT.

 

[Bobby Dazzler]

Nobody ever drive at 55mph unless it a very old vans or vehicles without MOT.

Lots of articulated tractor/trailors and vehicles towing travel at 55mph or a touch more. I know because I sit with them most of the time when towing!!

For vehicles restricted to 60mph on the motorway it's often easier and more relaxing to go with the flow, perfect with cruise control.

It's also a fairly stressful way to drive as you pretty much don't need to overtake, and so a surprising number of cars go in the same flow. If you pass at a higher speed you may not notice, but you'd be surprised.