My speedometer is +5kms out

[brad]

My mk2 VRS was out by 3ks at 100km/h, 4ks out at 110km. Always seemed weird setting the cruise to 115km/h on the freeway knowing you were still sitting on the limit. Ok-Ok - I might have usually set it to 120 knowing its unlikely I'd be pulled over in NSW for being 5 over

The vRs has the smallest speedo error because it has the biggest diameter tyre (225/40r1. 637mm
The 225/45r17 option is 0.4% smaller diameter. 634mm
The 205/55r16 is 0.8% smaller 631mm

It doesn't sound like much but it makes a km or 2 difference between each size

[KWICKS]

Speaking of Odometers, I've never had one correlate with those 5km road markets used to check your odometer. I always seem to run 100m to 200m past the last marker before 5km is added.

[brad]

when my speedo was 10% over and I had 205/55r16 I'd be at 5.3km at the 5km mark. Nice for Skoda service as it meant the 15k service was happening at 14,200km. It doesn't sound like much but it means the services come up a couple of weeks early. By the time you get to 150,000km you're half a service in front.

With the 225/50r17 at the 5km mark I'm at 4.8km so I've offset the inaccuracy.

I'm about to go to 225/40r18 - they'll be pretty close with the odo.

[Martin]

I'm about to go to 225/40r18 - they'll be pretty close with the odo.

I was wondering why am I one of the few with decent speedo/odo accuracy - but I am running the above tyres

[brad]

I was wondering why am I one of the few with decent speedo/odo accuracy - but I am running the above tyres

Going to 225/40r18 will make my odo more accurate but stuff up my speedo. Hopefully I'll be able to adjust it with VCDS.

I was aiming to go with 235/45r17 this tyre change but some 2nd hand 18" wheels & tyres came up at the right price so i thought I'd give them a try - I've had every other size.

[Gerrycan]

I like the odo to be accurate as it just makes true fuel consumption figures more easy to calculate.
Once I know what the speedo variation is then I automatically allow for it when driving. Just have to watch my speed when I drive another car though.

Now that most people have got GPS in car or on phone I think that more people drive at the real speed limit than they used to, and this is good.

[Fourwinds]

I guessed my speedo would be out, as most other vehicles are continually overtaking me. I ran a test using a mobile phone GPS, dash cam GPS, and our local Mr Plod (a good country copper) to test the accuracy of the speedo.


SPEEDO 60 GPS PHONE 57 GPS DASHCAM 56 LASER Nil Reading

SPEEDO 80 GPS PHONE 78 GPS DASHCAM 76 LASER 75

SPEEDO 100 GPS PHONE 97 GPS DASHCAM 96 LASER 95

So I will drive 3 kph over the speedo, and hopefully it will satisfy most of the tailgater out there.


Cheers

[Gerrycan]

Nice to know the Lasers are accurate and the display is possibly rounded down and not up.

[brad]

Fourwinds: If you know somebody with VCDS you might be able to tighten up the accuracy by modifying the distance impulse number.

This uses the impulses from the ABS (48 per wheel rotation) and the programmed diameter of the tyre to derive the vehicle speed. If the programmed diameter is different from the actual diameter then the speedo will be more inaccurate than it needs to be.

MB202 is the tyre circumferance. The DIN is the popup number in VCDS.

Coding digit: 1
DIN*: 22188
MB 201: 22188
MB 202: 1938mm

Coding digit: 2
DIN*: 22076
MB 201: 22076
MB 202: 1948mm

Coding digit: 3
DIN*: 21960
MB 201: 21960
MB 202: 1958mm

Coding digit: 4
DIN*: 21848
MB 201: 20660
MB 202: 2081mm

Coding digit: 5
DIN*: 22304
MB 201: 22304
MB 202: 1928mm

Coding digit: 6
DIN*: 22420
MB 201: 22420
MB 202: 1918mm

Coding digit: 7
DIN*: 22532
MB 201: 22532
MB 202: 1908mm

[Fourwinds]

Thanks for the info Brad.

I have Ross Tech VCDS cable and only ever used it to check for faults and to change the fog lights to come on when turning. I still learning and a bit hesitant to change any thing as I might stuff it up. On my next trip up to Greta, I might have to go via your place

Cheers

[rakehell]

Is it reading 5km at both 40kph & 100kph? That's odd because usually it's a percentage out.

Well I finally remembered to check and, you're right, it is a percentage. At 60kph it's 4km out. I'm not a real fan of having a tail so I'll stick to the GPS readings for now.

[spud75]

I drove a lot this weekend and noticed that my speedo is consistently reading 5km over my actual speed - according to my Garmin GPS and two "check your speed" gates.

Has anyone else experienced this? Is it something that built in or could there be another cause?

I wouldnt be using the check your speed gates for anything.

Drivers in Vic have still had to pay for fines when the gates said 100 and they were done for 105. The law says the gates are 'indicative' of your speed and not to be used to advise of actual speed. GPS on the other hand should be the most accurate. My A4 was 8km/h out compared to GPS. RS is about 6. And noticeably, the needle on the dial reads higher than the digital on the MFD.

[gldgti]

All vag group cars seem to be 8-10% out. Its normal. It stops you getting booked and improves your fuel economy.

[brad]

That might have worked 10 years back but if you know it's wrong because you've checked it with GPS & compensate then there's no point having an excessive variance. It's like people that try and get to meetings on time by setting there watch forward 5-10 minutes. It's a pointless exercise.

[gldgti]

That might have worked 10 years back but if you know it's wrong because you've checked it with GPS & compensate then there's no point having an excessive variance. It's like people that try and get to meetings on time by setting there watch forward 5-10 minutes. It's a pointless exercise.

Not if you haven't checked it. And not if your wife did it without telling you.