Petrol consumption vs speed

[gaz in sussex]

Off on our first half decent trip in a couple of weeks in the Explorer - Sussex to Blackpool. Round trip is around 700 miles - I was wondering does petrol consumption change dramatically with speed? Will I notice a big difference between say 65mph all the way and 80mph all the way?
I ride a motorbike to work every day - 60 miles each way and the difference between poodling along or caning it is about 2mpg! I think there will be a bit of a difference between a 250kg 1000cc bike and a 2 tonne 4000cc car though!

fatgaz

 

[shytot4x4]

Don't quote me on on this but I'd expect around 18 - 20 mpg at a steady 65 mph up hill / down dale. 15 - 17 mpg at a steady 80 - 85 mph.
What I do know is that after 10 or 15 miles of 65mph motorway driving you'll get bored and do the rest of the journey somewhat faster... (despite the pain in the wallet).

Simon H

 

[Ian5700]

Well i mean logic says the faster you go, higher revs, the more petrol you will burn.

The offical MPG ratings or 15.5 city and 25.5 highway, combined 20.1. The highway one is done at 56 mph, so as you go higher i would except a drop in mpg.

Using the cruise control seems to help mpg a lot, at least i find this. It stops you surging the revs and pulling and in increasing speed all the time. However maintaining 85 mph with cruise on, in anything other than light traffic is going to be near impossible, as you will always have that one that pulls out in front of you, and then you are just back to surging the revs again with the resume button.

 

[Minivek]

Speed definitely affects fuel consumption, mainly because of the boxy shape of explorers, aerodynamic drag "the force resulting from the wind pushing on the vehicle" is the main factor, this drag increases by a factor equal to the square of your velocity, so speed has a really big effect on drag, which basically "pulls" on the vehicle, impeding forward movement. There are other factor, like the fact these vehicles were built to be optimaly efficient at certain speeds, that's why you have your low profile sports cars, they cut drag a lot.

 

[gaz in sussex]

I realise its looks like a stupid question as I appreciate it will have an effect but I have done the trip several times in previous cars - 2 litre BMW 3 series (42mpg @85ish) and my beloved and then thoroughly nicked and trashed Subaru Impreza (27mpg @ just two figure speeds) and finally and the nightmare of all journeys in my 2 litre Frontera (27mpg@ 65-70). What I was asking and was neatly answered by shytot4x4 was if its 25mpg at 65 and 12mpg at 85 then its a no brainer - but if its 22 and 20 then its worth it as its still way cheaper than the train or flying or hiring a car. Just one other point - are the official figures based on U.S. or Imperial gallons as the city and Highway bits sound American rather than the Urban/Extra Urban you usually hear?

Thanks for the replies everyone btw!!

 

[Ian5700]

They are offical UK gallon figures from the handbook. 15.5 mpg (within city limits), 25.5 mpg (outside city limits) and 20.1 mpg (combined). If you have a handbook they should be listed in towards the back there along with the CO2 output, at least they are in my 1997 handbook.

The offical US gallon figures are 15 mpg (city), 19 mpg (highway).

 

[blueka]

I've just done a 340 mile round trip, sticking to 60mph on the tomtom (65 on the speedo) on the motorway with some urban driving too... I managed to get a return of 22.1 MPG... which I think is quite impressive...

Si

 

[shytot4x4]

That's more than impessive. It's stunning!!!

Simon H

 

[kands]

Hi all
In a previous life I was fortunate to have an Ex as a company car
I did over 125000 miles in it in 3 years, this included hammering up and down motorways and poodling about round town and on holidays (even towing an 18+ foot twin axle caravan about).
The average fuel consumption (worked out acurately for my expenses claims) was 22 MPG, this being fully 4 MPG better than my bosses 4.6 Rangie (which needed a new engine and 3 new gearboxes to cover a similar mileage ), so I think the fuel economy is pretty impressive to be honest.
I would agree with the poster above in as much as the MPG does not change drastically with different speeds, in fact mine used to burn more fuel when I used it for family holidays and was just poodling around slowly
The most expensive cost of driving at 85 MPH will be the ticket that drops onto your doormat in a few days, watch out for Big Brother Cam, they are everywhere matey :thumbdwn: Lastly, enjoy the trip

Keith

 

[gaz in sussex]

Thanks Keith - that was just the info I was looking for. I think I'll stick the cruise control on about 76 (should be a real 70) and just take my time. That way I might make it all the way there on one tank (just over 300 miles).
I use my motorbike a lot - 115miles a day and will have to remember that unlike the bike - cars have a front number plate so I cant ignore front facing camera or average speed SPECS cameras or unmanned camera vans or bridge cameras etc etc!! Maybe I'll go on the bike after all....

Thanks for all the posts guys

FG

 

[craigstevens27]

mpg

sorry to depress you all but ive just done a run to aylesbury and back doing 60 on the a roads and 80 on the motorway and the truck has returned 25mpg easily.my mate had one that returned 27on a run!

 

[ArtistsRifles]

sorry to depress you all but ive just done a run to aylesbury and back doing 60 on the a roads and 80 on the motorway and the truck has returned 25mpg easily.my mate had one that returned 27on a run!

Wish ours would get figures like that - we get around 20 solo doing 60 - 70 and 13 with the caravan on the back doing 55 to 60 ish.