Calculate actual combined mpg figures help please

Toxteth_OGrady

BackOnTrack wrote: »

Think I have identified it. The numbers quoted in the OPs 1st post relate to the percentage of fuel used in different situations not the percentage of distance travelled in different situations. Quite a subtle flaw really.

So if you use half your petrol urban driving and half extra urban driving then the quoted numbers are correct.

If you do half your distance urban and half extra urban then TOG's method is correct.

Yep, obvious now you point it out.

I suppose it depends whether you think 67% of the distance or 67% of the fuel is more meaningful.

If you were planning how much fuel you needed for a journey you'd probably use the 67% of the journey distance driven at mpg x and 33% of the distance at mpg y.

Lies, damn lies and statistics. :eek:

Toxteth_OGrady

I guess the result would be different yet again if you calculated it for driving 67% of time at urban and 33% of the time at extra-urban. :eek:

My brain hurts.

BackOnTrack

Toxteth_OGrady wrote: »

I guess the result would be different yet again if you calculated it for driving 67% of time at urban and 33% of the time at extra-urban. :eek:

My brain hurts.

He he yeah.

But there is nothing obvious about this stuff really. It's something you would never notice unless questions like these come up.

MikeyMacbeth

Yep, my brain was hurting too!

Little bit of background on why I was asking. Stems from this thread here that I started the other day.

Basically I've been working out my own actual historical mpg figure from fuel & distance I have travelled.

What I was trying to do was compare my mpg with the manuafacturers mpg figures based on the relative mileage of urban vs extra-urban driving I actually do as I know that 67% of my mileage is pure city commuting (urban).

From this I was hoping to derive an adjusted combined manufacturers (in the same proprotion of mileage that I do) mpg figure for the basis of a comparison to see how close to the manufacturers figures I was.

I know that it will be less anyway because the mpg tests are done under somewhat unrealistic conditions and also that older cars mpg tends to gradually fall away from their showroom mpg figures anyway.

It really is quite subtle and brain bending isn't it?:D

All this just so I could figure out whether it's cheaper to get the bus in to work or take the car!

Hey! now let's all just see if we can work a comparison method for all the 400 different energy tariffs offered by the utility companies for a bit of light excercise...

I'm going to have a beer now and cool my brain off... you can all have a virtual pint on me for the help :beer:

closed

Can't see the point in the comparison?

If you don't have a mpg computer in the car, brim it, drive to work for a week, brim it again, add parking costs if necessary, compare with bus, far easier. Then do the same again in winter.