Speedometer readings

[Stealthy]

Does anyone else get different speed readings from the digital and analogue speedometers?
My analogue reading is always higher then my digital reading (eg. 82kmh on analogue whilst 80kmh on digital).
Is there any way to fix this or should I take it up with the dealer?
Whaddya reckon folks?

[blutopless2]

its done deliberately by VW so that you should never be caught speeding.
dash indication on speedo will always be more than what the digital readouts etc show.
I looked into this a few years ago with a beetle. not worth the hassle to change it. I just learnt how far out it was and compensated with my driving.

[briseos]

you can fix it with some lateral thinking!

Found a fix for the analogue on my 2007 Eos - put 245/45 tyres on my 18"s and now the speedo is 100% accurate and my car looks hot as well!!

[Flipper Dog]

You got it right there with tyres/wheels.
The speedos are set to read slightly higher than the real speed for the fittment of their standard tyre/wheel set ups.
When you up grade to a larger wheel and tyre this will effect the speed and you are more on the correct reading. If you had the speedo set at say 15" wheels and you put your 19"s on then the reading would read under your actual speed leaving you open (and VW) to legal problems.

[Stealthy]

Okay I understand what you mean about changing the tyres and/or wheels but is that going to just correct the analogue speedometer reading only and have no effect on the digital reading? I can't see how.

[blutopless2]

When you up grade to a larger wheel and tyre this will effect the speed and you are more on the correct reading.

have not experienced this.
upgraded our beetle from 16" to 18" and the speedo is still out by the same.
It will depend upon whether they can match your original tyre circumference when they put on the bigger ones.

our jetta and polo are also upsized by 1" in the wheels/tyres and the speedos are out.

[Flipper Dog]

Okay I understand what you mean about changing the tyres and/or wheels but is that going to just correct the analogue speedometer reading only and have no effect on the digital reading? I can't see how.

You would think that the calibration of both speedo readings would match. They would have to take the readings from simular places unless you are talking about the digital display from the Sat Nav (RNS 510), if that is then the case than the GPS will be the more accurate one.
The analogue reading is the rotation of the tyre’s circumference where the GPS reads signals from the satellites which provide time over distance to give a speed reading.

By up sizing your wheels you not only increase your wheel diameter but you will normally go tyres with a greater width. The profile of your tyres is a percentage of your width so 205/55R 16 tyres are 16” wheels with a side wall of 112.52mm and the overall circumference of 1984.5mm. Upsize to say 255/40R 19 and now you have a 19” wheel, side wall of 101.85mm and over all circumference of 2156.7mm. That is now an 8% difference in your diameter. That will mean your speedo will read 92km/h at 100km/h (the 8% difference).

[Swallowtail]

Pretty sure you can adjust the speedo with VAGCOM.

Aha! Here we go:

http://www.my-gti.com/140/volkswagen-speedometer-error-correction

[DGen]

Actually not just VW that does this, all cars for Australia must show higher than actual speeds on speedo. New law in place about 18 months ago for Australia which makes this compulsory.

[cme2c]

I finally got to check this with my GPS GPS 100 km/h=digital speedo 106 =analogue 109.

118TSI DSG 16" standard wheels, Pirelli P7 205/55X16

[logger]

Mines GPS 100 km/h=CanBus/ABS 100 = digital speedo 106 = analogue 106. So digital & Analogue match for me which is fortunate.

[oileoi]

I'm planning to change the wheels of my car to 18" once it's deliver and I was wondering if the speedometer reading would change? How can this be adjusted on the VAGCOM

[logger]

I'm planning to change the wheels of my car to 18" once it's deliver and I was wondering if the speedometer reading would change?

Most probably not. Depends on the tyres you fit with the new wheels. Generally when you fit lower profile tyres to the larger wheels, the rolling diameter will stay much the same and no change to speedo. So specify tyres on your 18" wheels that match the circumference of your delivered tyres and it wont be an issue.

How can this be adjusted on the VAGCOM

It can be fiddled with, but not fixed with VAGCOM. But as mentioned you wont have an issue if you keep to your original rolling diameter.

[oileoi]

Logger, thanks for your answer the tires im planning to fit into my car are 225/40/R18 Y KUHMO 31 SPT.

Do you reckon the speedo reading will change at all?

[logger]

Logger, thanks for your answer the tires im planning to fit into my car are 225/40/R18 Y KUHMO 31 SPT.

Do you reckon the speedo reading will change at all?

What sort of car are you getting and what sort of tyres will it come with?

If for example you got a stock TSI118 it will come with 205/55/R16 and changing them to 225/40/R18 will alter your speedo by 0.8km at 100kmh which is trivial. Way less than the ~6% over read error that the car intentionally comes with. In fact this change should reduce the 6% over read to about 5% and is arguably an improvement.

Once you know what tyres your are replacing, use a tyre size calculator and it will let you compare the two sizes.