Rental car speedometer

If the car does not have tires on it of the proper size specified by the manufacturer the speedometer can be off from actual speed. With only 15K on it, probably not what is causing this off reading as the car should still have the original tires on it.

3 - 4 less than the GPS could get you speeding ticket since you drove the car a the posted speed according to the speedometer you would be over the limit. Glad to not hear someone calling this a conspiracy against tourists to generate revenue from speeding tickets! :-)

I miss typed in original post. Car was 3-4 MORE than the Garmin. We chose to use the car for our speed, and if we drifted over, then still probably within the speed limit. I guess time will tell.

Our Garmin always insisted that our last car was going slower than what the speedometer showed (by about 3 kph), as well. Yet it didn't show any variance when used in DHs truck. So I think it's a pretty big leap to accusing the Italian car rental agencies of tampering with all of their speedometers. To what end? Why would they care if you got a speeding get ticket? Answer: they wouldn't.

Any car I have had for the last decade or so always registers a slightly lower speed than my satnav states. It helps to avoid speeding tickets.

I don't use any kind of navigation device, but I occasionally compare what my speedometer shows with the speed that reads out on road speed devices, and it usually looks my car is going a few MPHs less than what my speedometer registers, assuming the roadside devices are accurate.

I believe that car speedos are calibrated so that the reading is never lass than the actual speed and may indicate 2% or 3% over the actual speed.

The car traveling slower than displayed would correspond to a smaller effective tire size. It could have been due to wear, or just a lower tire pressure, but likely because the car was designed that way. When you consider that is only a couple miles an hour, I doubt things are calibrated that close, since there is always some type of error. In fact, in Europe, a car cannot by law show a speed less than what the car is travelling, so any natural error must be skewed to the high side, or show you going faster than you are. Even that has a high limit, they cannot show a speed over actual of 10% + 4 km/hr, so at 80 km/hr; the speedometer is allowed to be off but must be between 80 km/hr and 92 km/hr. From what I have seen, 4 km/hr is pretty typical.

A couple of times recently I turned on Waze for driving on the highway, mostly for traffic alerts. I noticed that my speedometer and Waze often showed different speeds, oddly though, sometimes Waze was more, sometimes less. Technology, bah humbug.

All my cars always show 3 mph more than my sat navigation shows. The same is true with my rentals, also in the US. Maybe car manufacturers do so to save you a few speeding tickets.