Tom tom GPS speed reading accuracy.?

Question

My speedometer is out on my 93 gmc jimmy and i am about to drive across country with my tom tom and i want to know if the speed readings on my GPS is accurate enough to go off of? Please give best answers and any advice at all thank you alot.

Answer 1

I have been using a Tom-Tom since they first came out, and the MPH is almost dead on. My 720 is about 1 mph slower than my speedometer at times. I also bought a One for my son, and it is quite close as well. As long as you stay in the allowable buffer (5mph over) you should be just fine.

Answer 2

GPS time, position, velocity accuracy varies and is described as dissolution of precision.  It is effected by factors especially including satellite position at the moment.  I think you would probably do pretty well with it.  Stick with the flow of traffic, however. ;-)

Answer 3

Your TomTom speed reading is - in general - very accurate.  

However, it does calculate speed based on your 2D progress so if the road goes uphill or downhill significantly, the TomTom will under-report your true speed during that stretch of road.

If you're using your GPS as a speedometer, you should always err on the side of caution (e.g. if in a 70 MPH zone, try to stay about 66 MPH).

This is because car speedometers always over-estimate (the standards never allow speedometers to under-estimate, so the margin of error is always to have them report a faster speed than your doing).  So this means measuring 30 MPH via your speedometer you're always legal, whereas measuring 30 MPH via your GPS you may actually be over 30 MPH.