Brought my etrex GPS along to work this morning, comparing its speed readings with the cars speedometer. Ignoring error sources like GPS inaccuracy and tire preassure, I got fairly accurate readings (between 0 and 70mph). My car currently displays 2-2.5mph higher speed than the GPS at 65-70mph. Error seemed fairly linear with speed.

If my tire preassure is to spec I guess I have a 2mph margin for the CHP

/Elak

 

Comparing mine against my Magellan Map330, I found that the speedo reads about 1-1.5mph high anywhere between 70 and 80mph. Given that the the GPS reads to 0.1mph, and the speedo only reads to 1mph, I reckon that's pretty damned decent.

 

Using police radar and my g-tech i do know when it says 60mph, it's 60

 

With our GPS the RX-8 is 1.5 MPH higher than actual between 50-90MPH.

Vince

 

you have a police radar? Are you a cop?

 

anyone else done theirs? at 60, I hit the mile markers in just over 60 seconds. The only test I know to do. Does anyone know the statistical(not sure that's a good term - the engineering-based stated #s?) exact RPM for 60, or the exact speed for 3000RPM in 6th?

 

mentioned in another thread have been checking my speedo against a police radar "your speed is:" sign. the car speedo is consistently 1-2 mph faster than the cop radar at 45 mph.

 

He said he used a police radar, not that he has one.

Last time I got a ticket, the cop offered to let me look at the laser readout. I declined, since he seemed like an honest sort. And I knew damn well I was speeding.

 

At speeds up to triple digits, my speedo read approximately 2% fast when compared to my GPS.