Quote:
Originally Posted by wimorrison
The speedo is only a reflection of the number of times that the wheel has rotated and thus the distance traveled for each rotation of the wheel. The car is 'programmed' to expect a set distance for each revolution of the wheel and as the tyre wears you travel less distance though the car thinks you have gone the same distance and because of this the fuel consumption will appear to get worse as the car thinks you have used more fuel to cover the theoretical distance. The wear effect will be amplified with under-inflation, reduced with over-inflation ~ perhaps this over-inflation effect is the reason the high pressure (39PSI) is called the 'eco mode' 
As you suggest a GPS is needed to remove the tyre variation in the distance traveled and speed - many GPS will give you both instantaneous speed and distance traveled from a set point.
@volvorocks - clearly I missed your posts on the subject and I seek forgiveness. |
As you say the car is programmed to calculate speed from the tyre revolutions. But my question is, does this calculation then deliberately introduce the speedo over-read? I only ask because the distance traveled does seem to be fairly accurate?