Just for clarity.

Speedo can be out by up to 10%, but cannot over read speed.

i.e. you can be displaying 100kmh on the dash, but only traveling at 91kmh

You can't be displaying 100kmh on the dash, but traveling at 110kmh.

This of course implies you are running factory rims and tyre specifications. Changing them will change your speedo accuracy.

Also regarding how fast you need to be going to get done, I believe they are down to 1kmh, but usually it is 3kmh for a fine to be issued. Remember this is real speed, not displayed speed on your dash.

As Rossco said, plug a GPS speedo in and see what your actual difference is.

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[COLOR="Gray"]550Nm off a 2L... Just wish it was in the dak dak...[/COLOR]

I think you mean it can't under read ie. indicate a speed lower than what you are actually traveling at, they all indicate above (over) the true vehicle speed.

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Also be aware that GPS do read differently on occasions. I have up to 3 in the vehicle and they almost never read the same albeit only a Km out from each other.

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lol @ anyone trusting the speed read out of a cheap in car GPS system. They are not accurate enough to provide a completely 100% accurate reading! Those things have a target accuracy of +- 20m and only average out the speed based on rough GPS weypoints.. If the accuracy shifts, then the speed read out will be wrong. Only true way to measure speed is a radar speed gun, or a proper grade GPS with high accuracy satelite lock

Yeah that's what I mean. Me english gud speak.

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[COLOR="Gray"]550Nm off a 2L... Just wish it was in the dak dak...[/COLOR]

As long as it has locked on to a minimum of 4 satellites (most see 8 - 12) it is more accurate. all good units (navman, Tomtom & Garmin) use doppler (frequency) shift for speed & time shift for lat/long location & not way points.

lat/long accuracy is irrelevant, the system uses a totally different method to calculate speed over ground.

"GPS receivers typically calculate velocity by measuring the frequency shift (Doppler shift) of the GPS D-band carrier(s).

Velocity measured by a GPS is inherently 3 dimension, but consumer GPS receivers only report 2D (horizontal) speed on their readout. Garmin's specifications quote 0.1mph accuracy but due to signal degredation problems noted above, perhaps 0.5mph accuracy in typical automobile applications would be what you can count on."

.5 mph = 0.804672 kph pretty accurate no?

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for my line of work, no, that wouldn't be accurate enough (translating into units of measurement that would apply to my job.)

But for average Joe in his car trying to work out speed covered, I guess so.

lol kym, context?

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Needs more decimal points



Oh, and don't forget to carry the 2.

i'll let ya know..