AT tyres for 4Motion

[M36]

Great reads for exploring, to add to the discussion, measuring consumption with e.g. a 5% bigger tire seems difficult to compare/calculate with the onboard measures, isn’t it? E.g. if you read the same liters per 100 km with a 5% bigger tire it seems to be (around 5%) more efficient… does anyone have some background on this in relation to AT tires?

 

[WelshGas]

Great reads for exploring, to add to the discussion, measuring consumption with e.g. a 5% bigger tire seems difficult to compare/calculate with the onboard measures, isn’t it? E.g. if you read the same liters per 100 km with a 5% bigger tire it seems to be (around 5%) more efficient… does anyone have some background on this in relation to AT tires?

It would be difficult for the owner to calculate fuel consumption with different tyre sizes. If the circumference is altered away from the VW standard then there would be more or less wheel revolutions /mile or km. As the speedo accuracy is changed so would the odometer reading change. The simplest way would be travelling a known distance x times and measuring fuel used using a brim to brim measurement, because the measurement of fuel used by the vehicle remains unchanged but the distance travelled will depend on wheel circumference and hence wheel revolutions over a known distance and the vehicle doesn't know the known distance nor the tyre circumference unless you can update these values held in the vehicle computer used for the calculations.

 

[B J G]

It would be difficult for the owner to calculate fuel consumption with different tyre sizes. If the circumference is altered away from the VW standard then there would be more or less wheel revolutions /mile or km. As the speedo accuracy is changed so would the odometer reading change. The simplest way would be travelling a known distance x times and measuring fuel used using a brim to brim measurement, because the measurement of fuel used by the vehicle remains unchanged but the distance travelled will depend on wheel circumference and hence wheel revolutions over a known distance and the vehicle doesn't know the known distance nor the tyre circumference unless you can update these values held in the vehicle computer used for the calculations.

To back that up my , not too technically accurate, findings after a tyre aspect change from 235/55/17 to 235/60/17 was that on display mpg I had lost a few miles in mpg terms.

A check on road miles from Portsmouth Ferry Terminal to home by both Google & Tomtom is 164 miles. Check with the 235/60's gave 151 miles on trip. Never took actual note of mileage indicated on the 55 aspect tyres.
Applying an 8.5% correction to the displayed mpg put it back to, or slightly better than previous, figures.
Route that I take has variable traffic conditions which prevents a hundred percent accurate figure.

I travel at 70MPH and 60MPH as legally permitted.
previously had 73mph on speedo for GPS 70mph. now 69mph on speedo for 70mph.
Revs have dropped to under 2000 from approx 2200rpm. Ball park figures.