Originally Posted by caissiel
Get a GPS and it will tell you the true speed all the time, mine is off and everything is standard on it, My GM was right on the button. The Ford marks 100KPH and realy does 58.5KPH its not much but its 1 mile every 60 miles off.
I agree that a GPS is the best way to read the speed of the automobile, however some people don't like to turn them on every time they take their truck for a ride, or leave them in their truck for that matter. Also what if somebody borrows it and you need to know your speed - for me personally I just would rather have a corrected speedometer - but hey thats just me.
Based on the research I have done it looks like the vehicle manufacers can have speed readings that can be off by a little. Usually they make the speedometer read faster then what you are really going... why? So they (the automobile manufacter) cannot be sued when you get a ticket for speeding.
Now... one thing I am confused about... You said your ford marked 100KPH on the speedometer and you are really going 58.5KPH... well something does not add up here because thats almost off by 2 times.
No way can it be off that bad if it is a stock truck.