Just a random thought. May be some senior member may shed light upon it. (anjum, plz don't take it as the answer as that's rather a question 
)
My perception is, ODO measures speed by rev/unit time. For a car with stock tyre of 13 dia, ODO would be calibrated as follows:
Distance traveled per rev = pi*13 = 40.84 inches = 1.037 meters
so 100,000 rev per hour = 103.7 Km / hour
If the same tyres were changed with 14 dia tyres, ODO would be showing same speed for 100,000 rev per hour but in actual the speed would be
Distance traveled per rev = pi*14 = 43.98 inches = 1.117 meters
so 100,000 rev per hour = 111.7 Km / hour
If the above is true, then ODO might need calibration accordingly after changing the size of tyre.
And if above is true; For anjum, calibration of ODO might be out for some reason.
