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It is possible to reduce the use of petrol by up to 33% as a result of some simple economy measures when driving.
'What car' recently carried out tests on a number of cars to see the effect of speed on fuel use which can be summarised typically as follows:-
I have carried out the following practical tests:-
Long distance - 200 miles plus - manual V70 - speed generally 50 mph up to 60 mph ( 80 - 96 kph) - gently undulating country - air conditioning off most time windows shut - busy roads but no holdups - two people - measurement of mileage between full tank and full tank- increase in use from 29.5 to 38.87 miles per gallon (mpg).
Short distances between 1 and 7 miles - manual V70 - speed 30 to 40 mph (48 - 64 kph) - gently undulating semi rural area - air conditioning off windows open - busy roads - no passenger - increase from 26.6 to 35.64 miles per gallon (mpg.)
Speed was the most significant item that affected fuel use;low acceleration and use of high gear was the next significant. Previous speeds I drove at, naturally, were up to legal limits on roads, eg 70 mph dual carriageways and motorways and 60 mph non dual or restricted to 50,40 or 30 etc (UK.)
One has to change ones driving habit to using low acceleration and low engine speed, changing gear up at low speeds, so in the case of the V70 one can use 5th gear below 30 mph. This is not easy if you are in a hurry but the time lost overall can seem negligible. Tyre pressure was 30 psi.
Coasting. This is defined as depressing the clutch when gravity can propel the car, or slipping into neutral, allowing the engine speed to reduce. When fuel was rationed in years 1940 to 1952 in the UK coasting was common to preserve fuel and some cars had 'free wheel' devices, but nearly all cars were manual without hydraulics. In modern cars however with hydraulic brakes and steering there is the risk that with low engine revs if the engine stops when coasting, you will loose brakes and steering, so coasting is not recommended in the 'highway code' (or illegal.)
Advantages of economical driving 'by habit' are: Saving cost (£680 per 10,000 miles in above example) saving CO2, increased safety, relaxed and more peaceful driving experience.
