jono300

iTrader: (8)

Anyone advise me if the speed reading on a sat nav unit ( TT one v2 ) is generally regarded as being more accurate than the speedo in your car ? only ask as recently downloaded trip master for my TomTom one sat nav and find the speed reading is around 3 /4 MPH out compared to the cars speed. the other problem is that the readout does not update itself quick enough ie takes a few seconds before the new speed is recognised.

was thinking about going for an after market head up display unit but to be honest not 100% sure now what readout to believe to be the more accurate off the two ?

anyone else here run one off these cheap after market hud units. ? I see they now do displays which plug into the ecu port off your car.

richs2891

GPS from say a tom tom or a dedicated GPS source will gemrally be more accurate at a steady speed, but like say sometimes can be a bit laggy. A car's normal mechanical or these days electronic speedo will over read ie speedo shows 70 mph but only doing 67mph.
This is to allow things like varying tread depths on tyres - different tyre sizes for the same car eg 16" winter tyres 17 / 18 or 19" normal tyres etc.

Richard

billythekid

The GPS - as a rule of thumb - should be accurate to +/- 1mph in the "worst of normal" conditions but most companies will rate them to + / - 0.1mph these days.

You can of course get some really accurate GPS gear which will be *that* accurate but the price goes up quite a lot.

Most GPS Rx will have a refresh rate of 5Hz, but most of the software will only show updates at 1Hz. I think TomTom etc are running at 1Hz. I think this can slow down if the unit is doing other things too as CPU load goes up.

HTH.

jono300

iTrader: (8)

okay cheers for that. anyone else run trip master on there tt. ? or indeed any other hud unit ?

CREWJ

You will find that a car's speedo will read 5% higher than the real speed. As said it's for varying tyre tread depth but also to cover the manufacturer encase you get caught speeding and it's the fault of the speedo.