...that's another visit to my mechanic. I'll have it checked out and while I'm at it I have the wifes van checked out as well..
Don't bother to wast money.
On older cars there is a mechanical speedo cable take off via a small gear box and that ration can be changed at will. On newer cars they use an electronic rotation counter. Either of the above is tied in (for the sake of explanation) tot he rotation of the drive shaft.
If you buy a new car, drive exactly at the speed limit per your speedo and get a get a speeding ticket from your friendly police constable you just might sue the manufacturer/car dealer.
To err on the side of caution your actual speed will be somewhat less then what the speedometer displays.
Now, after driving a month your tires are slightly under inflated. Since the distance traveled is diameter times circumference you will be driving less distance per revolution of the drive shaft.
Now, to come back to the GPS, it does not know anything about your tires it just measure how fat you actually traveled in what length of time.
bassfisher6522 said:
I didn't realize that there was a speed display on these units. Are they pretty accurate with this feature. However, while it is a nice feature mine is off by 5 miles an hour according to my speedometer.
You will now see that it is the other way around, the unit isn't off by 5 miles, the speedometer is.
Just for info, while true speed is 100 km/h, my Taurus displays 102 km/h and my wife's Freestar displays 107 km/h .