Speedo reading accuracy

[LunchboxVRS]

With my MDF reading 110k the speedo needle is just a little over the mark and GPS is 103km. So I had a police friend bring his gun and he clocked me at 107. A week later when he had a different gun we did the same thing on the same road in identical conditions and he got me at 109.

So you can go with what ever you thinks best but there guns and fixed cameras are never spot on. There tolerances are tighter but the can still be about 3% off and be legal. as you can see if i went by GPS and increased by 7km with the second gun on me I'd get book for going 116km in tas it problem get of but from experience in Victoria I'd be pinged for sure. Had to tickets there for 4km over 5km over in a 110 zone on the Hume.

[DETROITCANDY]

I've found the same results, 117-118km/h = 110km/h, 106-107km/h=100km/h when measured against GPS, I haven't tried switching the snow tyre option on the MFD to correct it either.

As Bflat said, the cameras go off regardless with a barely visible flash of infrared light.

Be careful on the Hume, a few of the average speed cameras have now been upgraded to instantaneous cameras also (maybe one standalone camera has been added inbound?), always good idea to reset average speed on your MFD if you have one as you go past each camera to make sure your average speed isn't too high.

[Candyman]

Meh, just stop for a piss a few times and then drive like an idiot and average speed will be just fine

[trauts]

Same with my Polo
118km/h = 110km/h
106km/h = 100km/h
87km/h = 80km/h
All checked with GPS, It's highly frustrating. I've looked into places that will calibrate speedometers, but have had no luck.

[Ryan_R]

Displayed speed is 8% for me, those with larger rims (Golf GTI, R) have less variance.

I now have a Polar FIS+ which displayed the OBD speed which is the traditional 2kph out, much better. Also has a quicker refresh rate.

[Guest001]

Same with my Polo
118km/h = 110km/h
106km/h = 100km/h
87km/h = 80km/h
All checked with GPS, It's highly frustrating. I've looked into places that will calibrate speedometers, but have had no luck.

readerr0r tried to do mine but it didnt work in the Polo but helped a bit in the Passat

As I said above tyres wont fix it completely because they would have to be 40 mm larger diameter to bring it down 7kph and they would be illegal and put the gearing up toooooo much.
I now use the Canbus reading in the secret menuin the Passat when going out of town as this seems to agree with my TOMTOM as well

[trauts]

I now use the Canbus reading in the secret menuin the Passat when going out of town as this seems to agree with my TOMTOM as well

What is this Canbus secret reading in the menu? I'm very curious.

[ATYPIC]

As I said above tyres wont fix it completely because they would have to be 40 mm larger diameter to bring it down 7kph and they would be illegal and put the gearing up toooooo much.

FWIW I have 18inch wheels with 35 series tyres and the overall diameter is only 11mm more than the stock tyres on the factory 17inch rims and my speedo is bang on 100km.

[Guest001]

FWIW I have 18inch wheels with 35 series tyres and the overall diameter is only 11mm more than the stock tyres on the factory 17inch rims and my speedo is bang on 100km.

Maybe so but I used a tyre comparator and it gave me 40mm larger from whats on it but I only have a basic Comfortline

This one Wheel-Tire size comparer - RIMSnTIRES.com

[Ryan_R]

What is this Canbus secret reading in the menu? I'm very curious.

Despite showing you the wrong speed the car knows a more accurate speed (for the odometer, etc). If you have an RNS510 with customised firmware from here you can hold down the Setup button for ~30 seconds to get into a secret menu which tells you the OBD/canbus speed.

Or fit a PolarFIS if compatible with your car. Auto-Polar FIS+ Advanced - Complete Guide

Or buy a bluetooth OBD adapter + get the Torque Android app to display OBD parameters.


You can verify the difference by going on freeway, set cruise control to 100kph, then view the Average Speed display, hold OK to reset it and it will now show you the actual speed you are doing.