GPS Speed or Speedo?

[Stringent]

Just got an Origin B2. Looking at the speed on the Origin unit it is consitently about 3 mph slower than what my speedo says. So which would be more accurate?

[digit]

The gps will be more accurate, speedo's arent 100% accurate.

[XA04]

Yeah there was a discussion about this once before... but the speedo was faster not slower.

[steve threlfall]

Manufacturers set the speedo a little higher so the gps will be the most accurate.

[Howard]

The longer you maintain a constant speed, the more accurate the speed on the GPS will be (i.e not if you're in stop start traffic), but yes the GPS will be pretty much accurate. They set the speedos to an average to compensate for tyre wear, wheel sizes, etc.

When my speedo indicates 70MPH it's usually about 68 iirc

[Funkstar]

When this came up a couple of months ago, i tried to find the government guidelines for this. Speedos in the UK are allowed to be a certain percent out. I can't remember the firgures but basically a car is allowed to over report your speed quite a bit (10% seems to ring a bell) but can only under report by something like 3%

[integerspin]

I recently saw something about a london cabbie checking the GPS against his meter, the meter is calibrated to be correct withing a yard or so, GPS and meter were in total aggreement.
I saw a calibration cert with a recalibrated speedo and it had been set to be accurate at 30mph and it read something like +12% at full scale

[Stringent]

Oohh so I can overspeed by 3mph Woooo!

I do have 17" alloys, but when I redid the suspension, I had all the geomertry done as well, so that should have sorted it?

Well rather the speedo be faster so that it makes sure that people don't speed. Guess its a saftey margin. I find it logical, and yet silly.