Speed limit on motorways.

[swansonj]

i have a nissan mpv according to my car's readout it does 48 mpg at 70 mph around town it drops to 28 mpg.

Mmm, but that's not comparing like with like. The thing that wrecks the fuel consumption in a town is the frequent accelerations following halts. At a constant speed, that doesn't apply, and the optimum varies from car to car but is invariably less than 70.

 

[Tim Hall]

i have a nissan mpv according to my car's readout it does 48 mpg at 70 mph around town it drops to 28 mpg.

'Around town' and cruising at a steady speed less than 70mph aren't the same thing. It's the constant acceleration and deceleration 'around town' that makes the consumption suffer at slower speeds. Next time you're on the motorway, see what your consumption is at a steady 60 or 65.

 

[tommaguzzi]

so how is cutting motorway speed to 50 helping?
every time it s 50 on the m1 traffic backs up and we are traveling 30 to 50 accelerating and deccelerating all the time.

 

[TheDoctor]

The limit goes down *because* the traffic backs up. You're confusing cause and effect there.

 

[swansonj]

While we're talking about fuel consumption: cruise control was mentioned earlier. But cruise control - driving at constant speed - is far from optimum. You want to aim to keep the engine doing a constant thing so you want to have a constant speed on the flat but speed the car up downhill and slow down up hill. That's not AIUI what most cruise controls do.

 

[cyberknight]

Have ago at flying it yourself. How difficult can it be?

Hitchhiker's Guide to the Galaxy states: "There is an art to flying, or rather a knack. The knack lies in learning how to throw yourself at the ground and miss. ... Clearly, it is this second part, the missing, that presents the difficulties."

 

[Slick]

[QUOTE 4811016, member: 9609"]2.2td c class mercedes[/QUOTE]
At bigger engine will run at under 2000 rpm at 90 mph which is much more efficient than the example you quote.

 

[marzjennings]

So what stops you from doing that?

What, driving from Bristol to London in an hour, technically nothing. Been done in the past, will be done, I guess, again in the future.

 

[Dirk]

Journeys to Devon down the M5 always take forever.

I live in North Devon and travel up to the Midlands and back several times a year.
In the past 12 years I have only had one trip where I was held up for more than about 10 minutes on the M5.
I always get on and off at junctions 27 and 9.
Maybe I'm just lucky?

 

[gavgav]

Seriously, take the A49 via Shrewsbury, Ludlow, Hereford, then the A466 via Monmouth instead. It will take you the same time, if not slightly less, and be much more pleasant!

Just to warn that Shrewsbury is a car drivers nightmare at the moment, major roadworks causing untold delays. The M5 may be a better option!!

 

[subaqua]

'Around town' and cruising at a steady speed less than 70mph aren't the same thing. It's the constant acceleration and deceleration 'around town' that makes the consumption suffer at slower speeds. Next time you're on the motorway, see what your consumption is at a steady 60 or 65.

Yeah .

Towing the trailer I have to drive at 60 on the motorway . I get much better mpg than at 70 with no trailer.

So much so that lane 1 and 2 are my lanes of choice when not towing

 

[Dirk]

i have a nissan mpv according to my car's readout it does 48 mpg at 70 mph around town it drops to 28 mpg.

On a steady run up the M5 from North Devon to Redditch, at a steady 60 mph, I can get 69mpg in my Peugeot 207SW 1.6HDi.
Towing the caravan I get 32 mpg, or 46 mpg if I tuck in behind a decent sized lorry.
General knocking around, town and country, short trips, I get about 56mpg tank to tank.

 

[Slick]

[QUOTE 4811130, member: 9609"]it has little to do with engine efficiency and has nrarly everything to do with wind resistance, at 90mph it is the wind resistance that is using up vast amounts of fuel. No matter what engine you are using you will get many many many more mpg at 50pmh than you will at a 90mph.

why do you think it is more difficult to pedal your bike at 20mph than 10mph. why do you think drafting works.[/QUOTE]
I wasn't arguing with the mechanics of your theory, just the figures you quoted.

 

[Drago]

Wind resistance increases as a square of speed.

 

[gavroche]

Speed limits should be lowered to save lives, fuel and lower pollution.

That is a silly argument. Driving in 5th or 6th gear uses less fuel than lower gears so driving a slower speed, like 30 mph would be less fuel efficient and would considerably increase your journey time.