Speedo on my PD100 is atleast 10% out compared to GPS reading across the entire speedo range.

70mph is actually around true 62mph

139mph is actually 120mph

It's by far the WORSE or most inaccurate speedo on any car I've ever owned!

Anyway, is there anything that can be done to re-calibrate it to make it more accurate?

The wheels and tyres are standard 14inch steel jobs, and the tyre sizes match up to the fuel flap recommendations (185 65 14, I vaguely remember)

You do realise your GPS has an error margin of 5% dont you?

The only true calibration is via rolling road.

Fit bigger wheels. 17s with 215/40 have about +5% rolling radius compared to 14s. The cheaper alternative would be to fit a higher profile tyre in 14" form. I imagine you have 185/60 R14 as stock - mine did many years ago. Could perhaps try 185/70 R14, which would increase rolling radius by 6%. Just have to watch out for fouling the arches if the car is lowered.

^^^ That's the best excuse ever to fit bigger wheels!! You must oblige.

Fit bigger wheels. 17s with 215/40 have about +5% rolling radius compared to 14s. The cheaper alternative would be to fit a higher profile tyre in 14" form. I imagine you have 185/60 R14 as stock - mine did many years ago. Could perhaps try 185/70 R14, which would increase rolling radius by 6%. Just have to watch out for fouling the arches if the car is lowered.

Thanks for the reply

17's would be a no go. Want to stick to 14's on this car. It's used for work, so I love the soggy suspension and soggy ride afforded by the massive sidewalls!!

Fitting higher profile tyres sounds like a viable option. I wonder how much effect 5% rolling radius would have on performance. I'm guessing it would be quite noticeable?

You do realise your GPS has an error margin of 5% dont you?

The only true calibration is via rolling road.

Nope, GPS readouts on my Origin B2, mobile phone sat nav, and tomtom satnav - they are all showing exactly the same speed.

Nope, GPS readouts on my Origin B2, mobile phone sat nav, and tomtom satnav - they are all showing exactly the same speed.

There was a cautionary tale on BBC news site a while ago where someone tried to claim police reading was out based on their gps.

It was proved police kit was correct and the gps was out.

Nope, GPS readouts on my Origin B2, mobile phone sat nav, and tomtom satnav - they are all showing exactly the same speed.

Could be a coincidence given the relatively coarse GPS tracking in consumer level equipment compared to professional level? I can't remember exactly what accuracy consumer grade devices have but I seem to recall it's still in the region of 5-10 metres, as it's considered "good enough" and allows them to make the devices cheaply.

I'm quite happy with a little "cushioning" tbh

Matt

So I take it there is NO WAY of calibrating it using VagCom?

My 2 month old 'TomTom Start 25' reads a lower MPH speed than the car speedometer, by about 2 - 3MPH.

Rather believe speedometer and play on the safe side, rather than trust the TomTom stick-on ware.

Some of the replies on this thread just make me chuckle.

For what it's worth,

I once set off from my house in London to my friends in Leicestershire, 3 cars all driving in convoy, all filled up at same petrol station in London, all reset our trip computers there and then.

When we reached our destination some 110 miles later, ALL THREE TRIP COMPUTERS showed completely different distances... The skoda read something like 119miles, my friends brand spanking new Fiat Abarth showed 110miles, and my brothers 2007 Suzuki Swift Sport showed something like 113miles...

We all travelled in convoy nose to tail all the way... So not only does the skoda's speedo read incorrectly, but the ODOMETER will be out by the same % too..

So ok, it's a banger that I bought for a few grand, and probably will drive till it blows up (so total mileage reading will have no effect as I probably won't sell it) but I was hoping that there was a way to fix/make more accurate atleast!

Could be a coincidence given the relatively coarse GPS tracking in consumer level equipment compared to professional level? I can't remember exactly what accuracy consumer grade devices have but I seem to recall it's still in the region of 5-10 metres, as it's considered "good enough" and allows them to make the devices cheaply.

Still not convinced based on:

3 GPS readings all showing the SAME speed at a constant. that's not coincedence

Digital speed readout on my Golf R32's climate control (hidden menu) also correlates with the GPS reading, And the Golf's speedo read about 3mph slower than GPS and Climate Control. 3mph I can deal with, that's accurate enough.

but a consistant 10% across the range on the skoda is annoying.

3 GPS readings all showing the SAME speed at a constant. that's not coincedence

Chances are they all use the same chipset, so not really a surprise.

Signal bounce, screen deflection, and your car acting like a faraday cage etc will all add a margin of error.

As I say, you should only base speedo accuracy and get it adjusted against a calibrated rolling road. Speedo accuracy would be the least of your worries at your posted speed:

139mph is actually 120mph

So I take it there is NO WAY of calibrating it using VagCom?

Quite simply, NO.

Chances are they all use the same chipset, so not really a surprise.

Signal bounce, screen deflection, and your car acting like a faraday cage etc will all add a margin of error.

As I say, you should only base speedo accuracy and get it adjusted against a calibrated rolling road. Speedo accuracy would be the least of your worries at your posted speed:

So what about qouting my line about the Golf's digital speed readout (climate control panel) being EXACTLY the same as the GPS readouts?

So that's 4 devices (one being the car itself) showing that the speedo is incorrect.

Quite simply, NO.

That sucks