Which is more reliable..........

Question

my cars speedometer or my gps/sat nav? my car shows for example 30mph and my sat nav shows 27mph. Which one should I rely on?

Answer 1

You should be able to figure this out for yourself.  All you need is a stopwatch.

Locate a long straight flat section of interstate highway with measured mile markers.  Do this test at a time of the day when there is very little traffic on the highway.

Go to 60 mph on your spedometer and hold as steady speed as possible.  If the highway is flat, using the cruise control helps maintain a steady speed.

When you pass a mile marker, start the stopwatch. When you pass the next mile marker, stop the stopwatch.  Note the time and reset the stopwatch.

Now, repeat the test, only set your speed to 60 mph using your gps/sat nav.  Again, note the time.

Which ever one is closest to 60 seconds is the most accurate.

You may want to repeat each test a few times and average the results.

Answer 2

Speedometers have a high tolerance and show +5 percent on average (they should never show too little because of the obvious problems regarding speeding fines). I'm also sure car manufacturers like to pretend to you that your car is faster than it is.

GPS is usually much better.

Answer 3

I would rely on the highest registered speed and I can appreciate that many speedos do show incorrect speeds.

Answer 4

dont believe both look out for distance

Answer 5

sat nav in america a teenager got away with speeding fine due to sat nav recording his journey speeds.speedometers usually about 10% error