My speed on speedometer in my car differ from my GPS car speed. Which is more accurate?

Question

I have recently bought a satnav/GPS and found that the speed recorded on the machine differs from my cars speedometer. Which one is more accurate? Is this normal?

Answer 1

There are alot of variables that affect both the speedo and the GPS.

Speedo:

- age of the car

- factory size rims or have larger rims been installed

- have you changed the size of your tires (any dimension)

- How worn are your tires?  If you wear big knobby tires till they're bald that will really affect your speedo

- Is your speedo noticeably out of whack

GPS:

- how sensitive is it?

- does your GPS react to changes quickly?

- My Garmin Etrex Summit (v2.5 software and no WAAS) will be identical to my speedo when cruising but NOT while accelerating.  It's an older GPS that not very sensitive and doesn't react to changes quickly.

Anyway, these are some variables that can account for the differences.  

Answer 2

GPS; your car's is off, as is everyone's.

Answer 3

GPS. Yes, it's normal. All speedo's are off.

Answer 4

The GPS.

I have 3 gps and I compared them all.  The GPS are all within 1 mph (or less) within each other.

I did some research and it turns out that ALL cars have some error to keep you from getting a ticket because you thought you were doing 65 and you were really doing 70.  So it is always shows few MPH higher to slow you down.

good luck...

Answer 5

The average GPS is less than 1 MPH off at 60 MPH when your car speedometer can be off 5-10% just from tire ware changing the circumference of the tire which could put you off by as much as 3 to 6 MPH off. Most police department have a margin of 5-10 MPH before they cite you, so at a 65 MPH speed limit, they normally will not cite you if you are driving lets say 70-74 MPH most of the time.

Go with your GPS speed, it will be easier to fight in court! ha ha ha

I think there was a case where the father of a frequent speeder installed a video camera in his sons car pointing to the GPS and windshield, sure enough a cop gave him a ticket and the fought it in court, Radar and the cop words against a video and GPS. Did not know the outcome but it would have been interesting.

I would say the cop probably won but who knows! It's the cop job if he get caught lying and he has nothing to gain and everything to lose of reporting a driver for going faster than the driver really was driving and the judge will always side with the cop when they are in doubt.