Fuel economy.........

[brightmore]

Visited my son in Manchester at the weekend......drove there on the M62 from Leeds to M/chester a distance of some 45 miles at a nice 'dawdling' constant 60mph and returned a very satisfactory 59.7mpg.
On the same return journey, I did the usual 70ish mph and only managed 45.6mpg.....14 miles extra on a 45 mile trip.........a very big difference for getting back maybe 10 minutes quicker.
The car is a Peugeot 406 2litre diesel estate by the way.
Sadly with the caravan on the back, 29mpg is about par

 

[RayS]

Drag increases as the sqare of speed, not in a linear way. 'Speed' in this case means speed throgh the air, such that 60 mph roadspeed with a 20 mph tailwind = 40 mph while 60 roadspeed into 20 headwind = 80 mph. Drag will therefore change from being related to 60 x60 mph to bing related to either 40 x 40 or 80 x80. Run these through a calculator and you will be surprised at the differences.

 

[ProfJohnL]

I can certainly relate to the effects windage, Many moons ago I had to drive a luton bodied transit van from the west midlands to Felixtowe and back agains.
The journey down was fully laden and journey back empty, I cant remeber the exact fuel figuers but the difference was about 20% and apparnelty the wrong way round, I did better fully loaded than empty comming back. The main difference was the strong prevailing wind which was a NW. I also recall how much more the steering tugged on the return journey, requireing an almost constant bias to the right to offsett the winds effect.

 

[Gagakev]

So the moral of the story is you will never ever get a true reading, empty/full/headwinds/drags,etc etc, so why bother?
You/we obviously have the vehicles we want to do the job, towing, comfort, style etc, so IMO it is what it is.

 

[Lord Braykewynde]

The above is probably why I've never attempted to work out or worry how many miles to the gallon I'm getting since I bought my first car in the 60s.
As long as I don't find it excessive and I can afford to fill the tank I'm not going to get stressed over it.

 

[RayS]

In geberal I agree with LB's view (wouldn't dare do otherwise!) but theree are times whn you need to know some ida of mpg - a long tow across northern Spain on a winter Sunday being one - fuel stations few and far between on the autopista. The low fuel warning light is not a happy sight in these circumstances.

 

[Lord Braykewynde]

a long tow across northern Spain on a winter Sunday being one - fuel stations few and far between on the autopista.

I've never done that Ray and somehow I don't think I ever will

I did send for the winter brochures last year for Spain and Portugal. Despite my best efforts in persuasion and threatening to cut off her rations Her Ladyship isn't having none of it

 

[brightmore]

Thanks for that RayS.........very interesting....now where's that calculator????