GPS SPEED ACCURACY

roverron · Occasional Visitor Joined: Sep 18, 2004 Posts: 3

I have the excellent Tom Tom Navigator 3 with wired GPS on my XDA.
It shows my car's speed to be about 10% optimistic upto about 40mph, then 5mph optimistic from 50.
I know speedos usually over read by anything upto the allowed limit of 10%, so mine is probably typical.

Am I correct in assuming the speed via GPS to be very accurate at a constant speed (say constant for 20secs or more) since its derived from distance over time?

Dave · Posted: Sat Sep 18, 2004 2:14 pm Post subject:

Speed is only accurate at a constant speed, at a constant altitude (on the level) otherwise speed won't be 100% accurate. Speedo's are calibrated for a margin, but also speedo's are calibrated to the car with specific wheel sizes and full height tyres. As tyres where down, the more the speedo will drift out. We're only taking the odd mph here, but it's a difference never the less.

roverron · Occasional Visitor Joined: Sep 18, 2004 Posts: 3

Dave · Posted: Sun Sep 19, 2004 7:51 am Post subject:

It's always lagging by 1-2 secs so no I wouldn't rely on it 100% of the time. However it is more accurate than the speedo, but still it's not 100% accurage or anywhere close.

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