To those of you with GPS speedos

thefishdude

ive got a 2002 renault scenic diesel. when im doing 70 my tom tom sais 65mph

forgotmyname

Every cay will be slightly different, Changing your tyre pressures will affect the speedo slightly also. Different tyre brands have slightly different rolling diameters also.

Less air = smaller diameter so travels less than an over inflated tyre.

I wouldnt trust a satnav GPS, I have not yet seen one that can pinpoint my exact position when travelling at speed.

Yes they use GPS etc on track testing but they also use other telemetry equipment to make it more accurate.

TrickyWicky

vax2002 wrote: »

It measures flat distance, unfortunately roads have hills and dips, so sat navs are often a bit low.

No not really as they're more than capable of working out when they're moving up and down hill and calculating the speed based on that. Hills shouldn't mean anything to a nav. In the modern world, all the landscapes have been made into digital maps anyway.

bungle4by4

volvo s80, and its bang on the money.

AirlieBird

agrinnall wrote: »

Where can I get one of these sat navs that calculates what your fuel consumption is? :rotfl:

You can get an add-on for a Garmin SatNav here

The_ICT_Engineer

TrickyWicky wrote: »

What on earth are you on about?

The op isn't asking about driving a boat down the river thames. The op asked a simple question, when driving at a steady 70, what does your GPS speed say.

You have to go and over complicate it to try and look clever and instead you've made yourself look !!!.

Actual I own Dutton Commander, Which I can just drive into the thames.

brokenant

02 Peugeot 206 at 70mph shows 66 on the Tom Tom.
Shogun shows 68.
Not had a satnav on any bike but my early 90's triumph triple clocked 113mph at the speed trap at shakey with 122 shown on the clock.

epninety

#1 : 70mph - My daily driver Land Rover has an aftermarket VDO speedo, calibrated against the GPS.

#2 : 0mph on speedo when 70mph on GPS - My other Land Rover only does 70mph on a flatbed taxi :rotfl:

mikey72

vax2002 wrote: »

It measures flat distance, unfortunately roads have hills and dips, so sat navs are often a bit low.

forgotmyname wrote: »

............I wouldnt trust a satnav GPS, I have not yet seen one that can pinpoint my exact position when travelling at speed..............

GPS works out speed by doppler shift, not by position, so it works accurately up and down as well as forwards and backwards, providing it can see enough satellites.

Strider590

Wig wrote: »

Not Iphones with Apps

On a clear day when your nav can see the sky clearly and you are doing a steady constant 70mph indicated on the car's speedometer

• What does your nav say the speed is?
• If there is a difference what car is it?

Speedo dial = 78(ish)
OBDII reading directly from the cars ECU = 71
GPS = 70

Conclusive proof that the dial has been calibrated to show a higher than actual reading, whilst the car's ECU knows it's exact speed to be much lower.