FUEL ECONOMY QUESTION?

[londoner1]

car: 406 110 hdi Est
no towing and no weight in car.

I travelled to cambridge on m11 from london averaging 50 to 60 mph, the mpg reading (screen tab 2) reads 31.1mpg before i head off, i get to cambridge and it reads 37.8mpg which i stop.

Return trip, after 2 hours i head back to london via m11 and drive between 60-70mph and when i reach home the tab says 41mpg.

Is this correct??? Am i right in saying the mpg should at least read 50mpg going and coming??

Also can anyone here shed some light on the screen imgaes on tab 1 and tab2 ?

Your views are much obliged.

[DaiRees]

Tab 1 and 2 both tell you mileage, mpg and average speed since last reset. The other tab tells you "present" mpg and miles left in the tank.

Your readings from your trip will depend on when you last reset the info on tab 1 (do this by holding in the end of the wiper stalk). I tend to reset tab 1 with each fill up and tab 2 very rarely (only when I'm going on a long trip like last week), so number 1 shows your results for that tank full and #2 gives you a longer term view.

[Nicodemus]

To get 50 plus mpg you should drive like a grandad and do no more than 50 mph. I get 52.4 doing a gentle, 35 mile one way school run each day. Preferably no more than 40 mph and change gear at 1500 rpm with very, very gentle throttle foot.

As soon as you get up to 60 it will start to drop. 70+ will drop it back way down. Your figures are accurate as far as I can see.

Driving around town with a mix of one to four passengers (which I do at weekend nights but bear in mind less traffic after midnight) will get you 36 to 42 mpg in an hdi. Mine is a 90 tis true but I drove a 110 estate for some considerable time and the figures aren't that different AFAICS.

Weight makes a huge difference ( - 3 mpg typically with 3 pss'g's) so I never put more than half tank in mine unless going on mondo journey. As soon as you go to 3 or 4 passengers plus luggage everything goes to rat sh1t and you can kiss serious economy goodbye (i.e. less than 40 mpg).

If I had the dosh, that new Skoda Superb with the weird boot/hatch looks mega interesting...

Mind I've no money so it's a bit academic...

[mjb]

Weight makes a huge difference ( - 3 mpg typically with 3 pss'g's) so I never put more than half tank in mine unless going on mondo journey. As soon as you go to 3 or 4 passengers plus luggage everything goes to rat sh1t and you can kiss serious economy goodbye (i.e. less than 40 mpg).

Interesting. I've maintained 40mpg (average over several hundred miles non-stop) with both the V6 and tubby when fully loaded (3 adults plus camping equipment, beer, etc).

As long as you pump up the tyres up to compensate for the extra weight which you should do anyway, there's no extra load on the engine when driving at a constant speed on the flatish. It does however affect economy when accelerating.

[Nicodemus]

Interesting. I've maintained 40mpg (average over several hundred miles non-stop) with both the V6 and tubby when fully loaded (3 adults plus camping equipment, beer, etc).

I should've qualified by saying that was tootling round town at night. A run to east midfordshire airport (mostly busy old A roads with a fair amount of accel/decel) is about 50 miles each way and returns 44 odd loaded up and around 49 mpg empty depending on haste So your observation is bang on

Because loads are variable and unpredictable, one run a single person, next run four big uns and permutations thereof; tyres will usually be pumped to half way between min load and max load on most private hire/hackneys (except purpose builts and conversions). Sticker on my door pillar says same tyre pressure for all loads, but I have added a couple of psi at the back since I monitor tyre wear and noted some mild symetrical shoulder wear both sides at the rear.

[Welly]

@londoner1 - if you reset the average when you embark on the trip you'll get a repesentation of that trip rather than waiting for it to reward you for all your efforts

[mjb]

So your observation is bang on

Think about it - once a car is up to speed, what will cause it to slow down if you put it in neutral? Wind resistance which isn't affected by passengers and friction on the road which will increase with weight but can be compensated for with extra pressure.

Newton's second law of motion infers that the force (and thus fuel burned in a car) required to accelerate an object at a given rate increases with the weight of the object. Of course, the regenerative braking on cars like the Prius compensate for this a fair bit...

Because loads are variable and unpredictable, one run a single person, next run four big uns and permutations thereof; tyres will usually be pumped to half way between min load and max load on most private hire/hackneys (except purpose builts and conversions).

On an FWD car I'd go for moderate pressure at the front since the weight of passengers and luggage have little effect on the front axles (unless you have a giant get in), and pump the back up quite high for economy's sake