Just had a play with a friends GPS system and decided to see how accurate my speedo was.

The approximate error was -0.7Mph per 10Mph indicated.

The results were as follows(rounded up or down).

Indicated........GPS
30...............28
40...............37
50...............46
60...............56
70...............66
We drove to a friends private straight section of road
85...............79
90...............86
100..............93
110.............103

My wheels and tyres were standard with book PSI all round. Car was a MY00 with 14K miles.
GPS Signal was strong, with between 5 and 8 satellites locked onto. Several readings were taken and the average error worked out.

Not sure how much error to attribute to the GPS but now the US have switched off the fudge factor it's now about +-20Ft. Which at 60Mph is'nt much.



[This message has been edited by Neil Smalley (edited 07 January 2001).]

 

Neil I wouldn't worry about it. Just look at it that if your car indicates your doing the limit on a piece of road and a fine member of the local constabulary decides to follow you, your gonna be safe aren't you?
I think I read somewhere that manufacturers aim for a 10% higher reading than actual speed anyway.

 

A bit of an anorak question - but which GPS unit was it?..I've been investigating them a bit as they seem a good 'gadget'.

Do you know how often do they sample the position to get a speed read out - if thats how they work. Any idea how much of a non-straight line you can drive and still get an accurate measurement?

 

I use the Garmin eTrex unit linked to a 3com palmpilot running the GPSPILOT software. This isn't quite as good as the unit they ship with the wrx's (spoken command etc) but has a more professional aviator interface with touch screen buttons.

callum

 

Dunno. I can't remember I'll ask my mate. He uses it for navigation on his boat. The hardest part was keeping the needle dead on the speed indicated as it was very sensitive to the slightest movement of my right foot.

I was'nt worried about my speedo being out(cept if it under read) just interested in seeing how much it was out.

 

Lucky PC PLOD isnt around

 

The speed indicated on my 94 WRX seems to be well fast. Its got the little in-line convertor for mph but i think it's sided on the faster side than the actual speed bit quite a margin.
Will check with mates GPS, good idea.
Any others found this, and if so by what margin ?

 

<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:<HR>Originally posted by rapiddescent:
<B>I use the Garmin eTrex unit linked to a 3com palmpilot running the GPSPILOT software.[/quote]

callum,

i bought an eTrex, and although it is much quicker and maintains lock better than my old GPS38 (thats 12*parallel 'v' 1*sequential for you!), i am disappointed with the track-logs and general info available etc.

What extra stuff can the GPSPILOT software do (and how do you connect to a PalmV and how much)?

mb

 

MartinM,

i think that Garmin are the best for GPS - see