Fuels and their money

With the price of petrol now reaching prohibitive levels where many motorists are having to think twice about the necessity of their journeys or even using their cars at all, is it not time to seek advice from motor racing pundits on how we should fill our petrol tanks to maximise fuel efficiency. Although F1 racing has abandoned this season taking on fuel during races, there was, in the past, great emphasis paid to the tactics of how full should their car's tanks be to ensure they performed economically to maximise race distance and minimise pit stops. I certainly find that by keeping my petrol tank about half full, I achieve more miles per gallon. There must be automotive engineers out there who, given certain technical information about our cars, like their weight and power, can calculate the maximum amount of fuel we should be put in our tank to achieve the most economical miles per gallon results. Motoring organisations could compile this information for their members and make it available to others at petrol stations. I'm sure this would lead to a more economical use of fuel, be environmentally friendly and also spread the financial impact on our pockets.

Asked on 10 July 2010 by DH, Groby, Leicester

Answered by Honest John
A litre of liquid weighs about a kilo. 70 litres weighs about 70 kilos. So if you have a 70-litre tank, driving half full to empty will save you dragging around 35-70 kilos. Any weight saving improves economy. Disposing of a 'spare wheel' saves about 15 - 20 kilos. Apparently it’s also better to fill up on a summer’s morning rather then during the heat of the day. That way you get a denser fill.
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