how do you work out your mpg?

[Quagmire]

I use "Road trip" on my iphone, downloaded from the app store. Just tap in the reading on your trip counter, how much you filled up by (and whether it was a full or partial fill), and then put in the price per litre or total cost of the fill.

I'm using the "Lite" (free) version- this will only let you record mileage for one vehicle. The paid version i believe lets you record for multiple vehicles.

http://www.ituneappreviews.com/2009/01/05/road-trip-lite.htm

Apparently i'm currently paying 13 pence per mile running my 3.5 with single point LPG.

[Bowie69]

I do it in my head... divide the number of litres by 9 to fill, brim to brim, (easier than 4.5, most people know their 9 times table) then double it to get your gallons, and divide the mileage by that figure.

e.g.

63 litre fill, divided by 9 = 7

Double it = 14 gallons

200 = 140miles (10mpg) + 60 miles (~4mpg)

= 14mpg

^^ Clearly that's for a V8

I find it faster to do that than anything else TBH, plus you can do it whilst driving.

[maxtherotti]

Then why drive?

because im lazy

and its a new car to me so still has the must use it syndrome

and its too cold for the push bike

rob

[Landowner]

litres X .22 = gallons

miles divided by gallons = mpg

[Night Train]

OT

i used to work out my mileage quite accurately - and then i realised when i was using my gps one day that the speedo was out by about 10%.

I found that my speedo is about 3-4mph slower then my SatNav but the trip milage is the same. Do I trust the SatNav or the speedo for my road speed? I'm not concerned about breaking the speed limit as I don't speed but I would like to be doing 60mph with my trailer rather then 56mph.

[nicks90]

i trust the gps for both speed and mileage over my speedo and so should everyone else - especially if working out fuel economy.

But thats because i've had a few different tyres fitted to my 90 now, and although 3 of those sets were 265/75/16 - ALL of them have had different height and therefore overall diameters. Speedo and trip cannot be accurately gauged because of this simple fact.

when i took my old bfg muds off, they were 30.5" tall (fairly worn), yet the greenway machos measured 32.5" brand new! My old 7.50 firestone sats were over 33" tall.........

the gps lives in my car now and whenever i go on any long distance drives along our pleasant motorway networks - riddled with 50mph speed cameras, average speed zones etc - i ALWAYS use the gps speedo!

Unless you measure you trip via something completely accurate to work out your mpg, just calculating it via your speedo is purely a benchmarking tool for your own comparison and not necessarily realistic or accurate.

[maxtherotti]

my speedo is out by 3mph at 60 so not too bad (5% is ok by me) according to my garmin

but at least i now have a base to monitor the car from to see if any dramatic fuel increase happens

was more just curious really as i allways work mileage out per tank

rob

[Yostumpy]

HMMMM!!!!maybe the speedo isn't accurrate, but if you dont change your tyres every week, it still gives a guide as to how your driving, or how the trucks running. Drove up from kent to Buxton on friday, 65-70mph on m-way, got 25.9mpg. on way back drove more sedately, just under 60, home via cambridge on monday. picked up a 110 csw roof, strapped ot to my roofrack, and carried on my journey, but now slipstreaming a large lorry, 60mph. result? well suprised me! 31mpg.