You get a bit less mpg actual 10 to 20 % but petrol is £1.32 a litre & gas 72p a litre. it works out you save around 35 to 40 % on your fuel bills. Equivalent mpg is worked out by the price it has cost you to fill with gas, then calculate how many gallons of petrol you would have got for that sum & divide that into the miles you did on the gas. = your equivalent mpg. I hope that's clear.
I get mid 40's equivalent on my normal commute near 50 on the autobahn mid 50s if I really try 62mph.
I don't use the brakes (52.000 miles out of my last set of lexus front pads on my last ls400).
The easy way to look at theoretical cost saving is - at my local LPG £73.8 - Premium petrol £1.38 per litre => LPG is 46.5% cheaper than petrol. Factor in 73% efficiency and you have a 34% cost saving. I think 73% is a little conservative for a large engined car drived "nicely".
I believe my real world numbers are 4.171 miles per litre on LPG (on a long run 273 miles 65.39 litres - not being that nice)
I could get 420 miles out of a full tank of petrol (and be crapping myself) which is 5 miles per litre - ish.
Which gives 19.8% more LPG used - a rough calculation but is works out.
Another check - 400 miles on petrol would caost me £115.92 (84 litre tank) - 400 miles on LPG £70 - £46 cheaper on LPG = 40% cheaper - that does it for me. It is cheaper in the real world than the theoretical one.
Bren
My head hurts !!!!!!!
Is it cheaper then on LPG (I'm only joking) Mike
No, because you drive more, in fact everywhere any excuse