Calculated Mpg Vs Actual

[darrude]

So, I've seen a few time people mentioning the MPG read out might not be that accurate so I decided to do some (not very good) science.

Filled the car up, reset the trip computer and odometer.

After 552.3 miles (odometer) needed to fill up again, and filled 54.46litres. Trip Computer stated 49.1Mpg.

My Calcs:

Fuel Burnt: 54.46 / 4.55 = 11.97 gallons

552.3 miles /11.97 gallons = 46.1Mpg

Error margin 6.5%.

I also checked the mileage by checking my route to on my longest journey this fill up Vs Google.

Odometer reading 57.1miles

Google journey length 60.1miles

Assuming Google is correct then the odometer on current tyre diameters (treadware/pressures) is underestimating by 5.3%.

so the actual MPG is (552.3*1.053)/11.97 = 48.6Mpg (1% margin of error)

One thing to note is I switched to winter tyres half way through the tank of petrol and only did the odometer check on brand new snow tyres, so don't know what the error margin was on the summer tyres. I reset everything so will check again next time I fill up!

[ColinBarber]

What size are your new snow tyres and your standard ones?