Speed measurements

aardvaak

If I am driving along at say 30 MPH my Sat Nav says about 24 MPH which is the most accurate speed?

mikey72

Satnav



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aardvaak

mikey72 wrote: »

Satnav

Not that I have been caught or have a gripe does the Mobile Speed Vans calibrate their equipment on Sat Nav data and figures?

vikingaero

On a flat straight road on a constant throttle the satnav is more accurate.

On older cars with cable drive speedometers the indicated speed can be really vague. Now that most cars have speed pulses from the ABS wheel sensors the speedos are better.

mikey72

aardvaak wrote: »

Not that I have been caught or have a gripe does the Mobile Speed Vans calibrate their equipment on Sat Nav data and figures?

I would assume they have a purpose built calibration machine that tests the frequency of the pulse emitted, and checks what speed is shown for a signal sent back to the detector.
The equipment must have a calibration scehdule, and must be carried at the set times.

agrinnall

I occasionally test my speedo and satnav speeds against a radar controlled sign that displays your speed, every time the satnav is a lot closer than the speedo.

Retire

I used to have an old banger and when the speedo was showing 70 my sat nav showed 63. In fact at various speeds my speedo was about 10% slower than my satnav. 30 speedo sat nav 33.

I used to wonder why everyone was passing me on the motorway.

I bought a new car and my speedo and sat nav are almost the same. speedo shows 70 sat nav shows 69.

brokenant

Satnav without a doubt. My 94 triumph m/c was showing 125mph on the dial when the actual calibrated measured speed was only 113mph, almost 10% out.

Gloomendoom

agrinnall wrote: »

I occasionally test my speedo and satnav speeds against a radar controlled sign that displays your speed, every time the satnav is a lot closer than the speedo.

Those things can't be relied upon to tell you how fast you are going. I pass two on my drive to work. One flashes at 28mph on my speedo and the other at 32mph.

forgotmyname

Most satnavs i have used cannot place your position exactly so they are a few feet or even metres out.

How can you say thats more accurate than a speedo?

Yes Yes... Magazine testers use GPS systems to test speed, But they also use road speed measuring equipment to
back that up to make it super accurate. And they dont use £50-£200 satnavs.

£££££.

reeac

forgotmyname wrote: »

Most satnavs i have used cannot place your position exactly so they are a few feet or even metres out.

How can you say thats more accurate than a speedo?

Yes Yes... Magazine testers use GPS systems to test speed, But they also use road speed measuring equipment to
back that up to make it super accurate. And they dont use £50-£200 satnavs.

£££££.

This is the point when someone usually brings up the issues of tyre wear and inflation pressure.