LPG is about 15% less efficient than petrol as it has a lower calorific value...
I run LPG and I average 15.3 on LPG, computer regularly returns 18mpg. 15.3/18 = 0.85
I don't work out the equivalent in a theoretical MPG, I work it out as Pence per Mile...
On LPG I return 22.3p per mile @ 15.3mpg
If I was running 250 miles on Petrol at 18mpg at £1.31p/l that would be:
250 / 18 = 13.89 gallons
13.89 x 4.54 = 63.06 Litres
63.06 x 131 = 8260.86 pence (£82.61)
8260.86 / 250 = 33.04 pence per mile
If I was to work out the equivilant:
Petrol Price = 131p per litre
LPG = 72p per litre
72 / 131 = 0.5496
15.3mpg / 0.5496 = 27.8mpg
But it is not a true figure and is purely theorectical and means nothing really....
Price per mile is a more accurate way of judging cost saving
Try explaining that to Martyn. Oh you just have.