The great fuel consumption poll

[844PHW]

Originally Posted by Harvey1512

.....
go onto any car forum and you will find threads where people are angry that their cars get nowhere near the professed mpg figures. It is a problem across the board and one that govt seem quite happy to allow. Very odd.

It means that car drivers blame the manufacturers for something/anything, not the government.

[TheRapidRooster]

Hi to you all. Is this poll about what the optimistic on-board computers tell us or is it about actual and physical calculations from Neck to neck fill-ups?

Also I cannot see the D5 SE Geartronic on the list. Mine is a 2005 (05) variant.

[wimorrison]

The platform is shared between the cars in the grouping which started with the XC60' in 2008' your car is 2005 which has its own grouping which you will find here

[m2srt]

My D5, if I drive like a vicar, can get respectable MPG. I can see upto 6.5l/100km on a steady trip. I've started using litres instead of gallons as that's the way we're charged for our fuel and I've become accustomed to converting miles to kilometres. Anyway, what I wanted to say is that as I'm keeping my XC60 until the next gen '60 and I only do 6000 miles a year, I think I'll just enjoy my last few years with a burbling 5 pot and not worry too much about it's drink problem if driven in an un-saintly manner.

[RoyMacDonald]

Originally Posted by jimbg

The speedo may over-read by 10%, but the distance does not!

Otherwise over a 100 mile trip, it would show 110 miles and it most definitely does not.

I had been thinking the over reading of the speedo must carry over to the distance as well, but reading the handbook it says that every time you change the tyre pressures or tyres you need to set the tyre monitor in "My Volvo" to "recalibrate" and drive a certain distance otherwise the size of the tyres will be wrong and the tyre pressure monitor won't work correctly. So if the car always knows what size the wheels are, that would account for the distance being always correct.

[id5]

Originally Posted by RoyMacDonald

I had been thinking the over reading of the speedo must carry over to the distance as well, ....So if the car always knows what size the wheels are, that would account for the distance being always correct.

I do not think that the distance is correct. I think that the wheel calibration is separate and just cares about the difference between the old and new wheels.

[RoyMacDonald]

Originally Posted by id5

I do not think that the distance is correct. I think that the wheel calibration is separate and just cares about the difference between the old and new wheels.

I went through this on another thread and the consensus was that the milometer was accurate. That couldn't be the case unless the wheel size was accurate. Doesn't just apply to old and new wheels it applies to changes in tyre pressure altering the size of the wheel.

[id5]

Originally Posted by RoyMacDonald

I went through this on another thread and the consensus was that the milometer was accurate. That couldn't be the case unless the wheel size was accurate. Doesn't just apply to old and new wheels it applies to changes in tyre pressure altering the size of the wheel.

I agree that the milometer is the most accurate method of measuring the long distances a car travels over a road that is not straight but it has a wide margin of error that works out to about the same as the speedo.

One problem is that wheel sizes are not accurate for example the difference between Continental R17's and R20's for an XC60 is approximately 65 metres per kilometre, given the difference in the tyres maximum outer diameter and the given 4% error margin of the rolling circumference from maximum to minimum.

The tyre pressure monitor does not know the size of the tyre or its rolling circumference, there is nowhere to add this information into the system when a wheel is changed, and unless the car was to have a sat nav it has no other comparative method of measuring distance to tell if the wheel size has changed, it can only measure the rotational differences between each wheel.

[RoyMacDonald]

Originally Posted by id5

I agree that the milometer is the most accurate method of measuring the long distances a car travels over a road that is not straight but it has a wide margin of error that works out to about the same as the speedo.

One problem is that wheel sizes are not accurate for example the difference between Continental R17's and R20's for an XC60 is approximately 65 metres per kilometre, given the difference in the tyres maximum outer diameter and the given 4% error margin of the rolling circumference from maximum to minimum.

The tyre pressure monitor does not know the size of the tyre or its rolling circumference, there is nowhere to add this information into the system when a wheel is changed, and unless the car was to have a sat nav it has no other comparative method of measuring distance to tell if the wheel size has changed, it can only measure the rotational differences between each wheel.

How do you know that the computer cannot work out the size of the tyre?

Dam thing knows I am running on different size tyres and adjusted the speedo accordingly because I tried to correct the speedo error with a different size tyre and it still reads exactly the same error.

[id5]

Originally Posted by RoyMacDonald

How do you know that the computer cannot work out the size of the tyre?

...

Because it has nothing to measure the size of the wheels with, it only has the ABS rotation sensor.