GPS Owners: How well does your GPS track speed on the road?

I have a MAgellan Roadmate 1440, and I'm finding it to be pretty poor compared to my 3 year old Maestro (which, sadly, was stolen when my car was broken into...).



Anyway, I'll be going down the highway with the cruise control and the GPS will indicate a speed change every 2 seconds. 110 109 110 108 109 108 110 111 108 109 115 110... (km/h) all within the same ballpark, but it's terribly annoying to me because it keeps catching my attention. I distinctly remember this not happening with my previous unit...



I'm wondering if this is pretty standard for a typical GPS, or if maybe I have a defective unit, or if maybe I bought a cheap model? (I have run all the updates available already)GPS Owners: How well does your GPS track speed on the road?
My Garmin is dead on so far as I know. I have had 2 Garmins and feel this is one of the top brands. My first Garmin didn't show much change in my speed when I was on the road. My current Garmin does. Like yours, it shows a variation of plus or minus 1 MPH for the most part. Going up a steep hill will show a slow down maybe 2 MPH until the cruise control and vehicle mass can catch up to the hill. You should expect some variation in your speed. Even using cruise control your speed will vary to some extent. A slight rise in the road, a breeze either for against you, the draft from the vehicles going the other way, will all change your speed slightly. Cruise control can't prevent this. It takes some time for it to react and your vehicle mass also will take some time to change for the change if power from your engine. The changing speed shown by your GPS would mean it's measuring your speed faster than your cruise control. I would say your old unit, the Maestro, didn't do as good a job of measuring your speed as your current unit. Improvements have probably been made in the circuitry between the older units and todays units that let them measure the speed with a higher degree of accuracy.GPS Owners: How well does your GPS track speed on the road?
I have a two Garmins, a 60CSx hand held and a Nuvi 650 both match the speedometer in my Jeep. Your cruise control is not going to be dead on, it's going vary 1 or 2 km/h up and down.GPS Owners: How well does your GPS track speed on the road?
I'm using a Garmin Nuvi 205, bottom of the line, and it is as accurate as the satellite will allow.



The satellite send a data stream and the receiver decodes the data. The receiver receives multiple satellites at the same time and uses the data to give you you lon/lat, HASL and GS (ground speed) - as well as other things such as UTC time.



The quality of the receiver, the sensitivity of the receiver, determine a lot, as well as the built in inaccuracy that can be toggled by the ground stations.



I have checked my Nuvi using a Motorola SiRF III GPS engine and map program, the Nuvi is dead on. I have also checked using the GPS receiver in my Nokia cell phone and found that the cell phone is not as accurate. Poor antenna, poor software.