vehicle speed

[collaboration]

what's more accurate?

navman vehicle speed or dash?

got 20" rims on my car and the stock supposed to be 17" and i just realised today that the two speeds are off by almost 10km/hr???!???!?? dash is showing 10km slower

i don't want to be flashing cameras everywehere i go..

[Guest boostcut]

navman by far. change back to 17s and find out ;D

[aim]

The Navman should read a slower speed, but yeah the wheels could screw that up a bit

[Sudo]

I'm trying to work this out myself.

I've got a Tomtom 720.

Stagea w/ 18s @ 100 TomTom @ 88

Forester w/ 17s @ 100 TomTom @ 92

Primera w/Stock @ 100 Tom Tom @ 100

Golf GTi w/Stock @ 100 TomTom @ 102

So think tomtoms the correct one. I asked a cop, and he said only military units are correct and to watch my speedo but yeh.

[wrx_lou]

Back in the day when I had my deisel hilux, I used to use the rev counter

[DRFVDR]

 Sudo said:

I'm trying to work this out myself.

I've got a Tomtom 720.

Stagea w/ 18s @ 100 TomTom @ 88

Forester w/ 17s @ 100 TomTom @ 92

Primera w/Stock @ 100 Tom Tom @ 100

Golf GTi w/Stock @ 100 TomTom @ 102

So think tomtoms the correct one. I asked a cop, and he said only military units are correct and to watch my speedo but yeh.

Only a correct statement regarding positioning,but as the speed u travel is the same whether your position is a few metres out(and i think this is only true when the americans are at war and put in place a "differential" for GPS positioning) or not then the speed that is being shown by your GPS navigator is 100% (or near enuff) correct.

I have 2 nav devices in my Landcruiser (one a navman for directions and one a plain old gps for position ) and they both display the same speed at the same time where as my speedo is 10 km/hr out at 100 km/hr(which is only just legal as u are only allowed a 10% wrongness )

[Koom]

Nothing is ever 100% correct..........

[DRFVDR]

ok it is 99.9999999 % then

[Koom]

Is that accounting for continental drift and plate growth in regards to the position of the satellites?

One too many 9's after the decimal I reckon...

[DRFVDR]

heheheh if the GPS sat's keep falling outta the sky/colliding with space junk,GPS may not work for much longer

[funkytown]

 DRFVDR said:

gps for position ) and they both display the same speed at the same time where as my speedo is 10 km/hr out at 100 km/hr(which is only just legal as u are only allowed a 10% wrongness )

and overall rolling diameter of wheels is the region of 5-6% over or under from factory yer?

[QRAF]

 wrx_lou said:

Back in the day when I had my deisel hilux, I used to use the rev counter

Someone didn't like paying for RUC if i unplug my ciggy lighter in my dash my speedo doesn't tick over either, but being a petrol this has no benefits as i already have high km's

[subieboy]

 Sudo said:

I'm trying to work this out myself.

I've got a Tomtom 720.

Stagea w/ 18s @ 100 TomTom @ 88

Forester w/ 17s @ 100 TomTom @ 92

Primera w/Stock @ 100 Tom Tom @ 100

Golf GTi w/Stock @ 100 TomTom @ 102

So think tomtoms the correct one. I asked a cop, and he said only military units are correct and to watch my speedo but yeh.

That is correct - only Military GPS devices are accurate to within 10m (if you are lucky)

The US controls something like 90% of all GPS satelites.

US law states that only US military (and its allies, etc) can access more than 3 satellites at any one time. Your GPS may say its connected to 20+ satellites but it will only be actively talking to 3!

Commercial GPS devices rely on software, some complex algorithms (and some magical stuff like supposition/magic/allowances/etc) to determine your speed and location.

As for accuracy of speedometers... by law they have to be accurate to within 10 %, but they are also restricted to over reading (i.e your indicated speed is 100, but you are actually only doing 95), and they are also subject to wear n tear from the cable/tyres/drivetrain/or other method it uses for measuring speed...

Rely on your speedo thats why it is there...