Speedometer inaccuracy Question

Third Opinion · 4 Dec 2006 at 20:37

Doing a steady speed over a distance of miles my GPS has indicated my speedo is inaccurate. At 70mph the GPS calculates the speed at being more like 65mph. I moved the unit into the wifes car and that appears to have an accuracy about 1-2mph out at 70mph.

So my question is this: if my speedo is out does this mean the odometer is also out? So if I travel 70miles on my odometer I have only covered 65miles real time?

This would mean all my travel expense calculations and MPG estimates to be wrong.

Axeboy · 4 Dec 2006 at 20:46

I wouldnt worry to be honest.

I found the same when testing various cars at work, they were all out by about 3 - 5mph @ 70mph.

Most cars are the same, surely its not a huge deal?

BennyC · 4 Dec 2006 at 20:47

hmmm, would that affect you when going thru speed cameras etc etc then? just wondering.

Type_R · 4 Dec 2006 at 20:49

Well from what I know, my MK5 GTI reads exactly 10% - yes 10% more speed then I am actually travelling at. However the computer calculates the mileage spot on and mpg/average speed etc are based on your 'true' speed. Hence I would assume the mileage on my car is 'true' rather than based on the overspeed of the speedo.