Speedo accuracy

[Amchlolor]

Just wondering how accurate the A3 speedo is, compared with satnav/GPS readings?
I was in a borrowed 1.6Fsi Golf to Manchester and back this weekend, using a borrowed Tomtom.
Assuming the Tomtom is accurate, the Golf's speedo was hopelessly inaccurate.
An indicated 55mph was a true 50mph.
An indicated 90mph was a true 82mph.
So this thing was right on the 10% limit for speedo accuracy.
I ended up ignoring the speedo and looking at the Tomtom readout.

 

[vrbob]

I was wondering this too as i have sat nav on my phone and when i am driving in my 8L S3 it seemed to say almost exactly the same as you got with the Tomtom in the golf.

 

[h5djr]

My previous A3 was almost 9% out compared with my GPS, but my current 170 is almost spot on. Seems they do vary quite a bit.

 

[Kontraband]

the faster your going, the more out it is seems to be the general rule on gps v speedo.

Wouldnt be surprised if speedos are slightly under calibrated as they only have to be accurate to 10% at 30mph for cars.. from memory. no issues of being sued or whatever then for dodgy speed readings.

 

[Amchlolor]

Wouldnt be surprised if speedos are slightly under calibrated as they only have to be accurate to 10% at 30mph for cars.. from memory. no issues of being sued or whatever then for dodgy speed readings.

They have to be 10% accurate right through the speed range, not just at 30mph.
They are only ever allowed to over-read too, never under-read.

 

[N8]

After putting alloys on etc, the speedo goes out, where would you get it re-calibrated??? Anyone?

 

[Kontraband]

aye, 10% throughout sounds right.

 

[Matt]

Not put the TomTom in this car yet. My old Corsa (with 17" alloys instead of 14") read spot on with the Sat Nav. Think the larger wheels must of corrected the speedo?

 

[JohnS3]

I tested this recently with the RNSe in engineering mode to get the GPS speed compared to the DIS digital speedo. It was quite accurate even up to motorway speeds. Never saw more than a few MPH difference.

 

[Amchlolor]

After putting alloys on etc, the speedo goes out, where would you get it re-calibrated??? Anyone?

I wouldn't bother, I reckon you'd still be better off with a cheap satnav.

 

[N8]

Cheers Bowfer

 

[Amchlolor]

Quick google search for 'speedo recalibration' throws up some dodgy looking 'mileage correction' services.
I knew this went on, but I didn't know you could source it on the net!

 

[bacardi]

my GPS shows 80 at a speedo indicated 82 - quite pleased with that

 

[Amchlolor]

Is there any variation between GPS systems?
Are some more accurate than others, or can you take it as read they're all accurate?
I must admit, it was quite freaky setting the cruise control (yes, a poxy 1.6Fsi Golf has cruise control...) at an indicated 90mph, knowing I was only actually doing 82mph.
It was like f***ing with my brain, man...

 

[Deleted member 22276]

tested my s3 with tomtom and cruise control across a large range of speed on the german autobahns, 6% overread. So the 166mph I managed was actually only 157!

 

[bacardi]

most portable integrated GPS systems are pretty much of a muchness, I've had the same indications from Nokia N95's, N82's, N958GB's, E90's and also HTC Handhelds (MDA Compact III, Vario III's) along with Tom Tom's and Garmin ones
Only a couple of times, with GPS dongles have I seen some slight differences

 

[MarcQuinlivan]

When I set my cruise to 130km\h for motorway driving my RNS-e, Garmin Nuvi 660, and Nokia N95 8GB with Garmin Mobile XT all show 126km/h, so that's about 5 and a bit percent over. My BlackBerry Curve shows 122km/h for some reason. You can't imagine the fun I have when I come to a junction and all those units tell me to go in a different direction!

the 10% tolerance is across the board - although logic would suggest that if it is 10% out at 30mph then it is also 10%out at 100mph.

 

[RobB]

Mine is only about 1-2mph across the speed range. This is using a Tom Tom and another piece of GPS kit. At 120mph in Germany it is still almost spot on. The recent showing of those speed reminding flashing signs in residential roads also show that a true 30 is 31 on my speedo. My previous 3.2 was slightly less accurate but still only about 5% out.

 

[RHODIE]

My 3.2 is about 10 % out too. Very odd going past a speed van at 80 with gps saying 72/3.

 

[MarcQuinlivan]

My dad picked up his new GTi last week and was telling me that it seemed slower than his old one.

I set him up with a digital (uncorrected) speedo on his climatronic unit and went for a test drive. At 120km/h on his analog speedo the uncorrected digital version was showing 110km/h. My A3's true speed is 126km/h when the speedo shows 130km/h. He double checked it yesterday after installing his MFD2 navigation (VW's RNS-e) unit and it showed 119km/h when his speedo showed 130km/h. His Garmin Nuvi also read 119km/h.

For those of you not up on their kilometer conversions.

My dash reads 81mph, my actual speed 79mph.
My dad's dash reads 75mph, his actual speed is 69mph.
My dad's dash reads 81mph, his actual speed 74mph.

I've looked into it and apparently all GTi models have this problem. I even found a TSB (Technical Services Bulletin) from VW of America which explains the problem, and tells the dealers how to resolve the issue and claim a refund for the warranty work to carry them out. It says that the issue is for all cars built from September 2006 for 12 months. Logic would suggest that any cars built after September 2007 would have the problem fixed. That appears not to be the case.

The fix can be done via VAG-COM, so I'm going to do it for him later in the week and see if it fixes it.

One downside to the issue is that for every 108 miles\kilometers his odometer reads he's only doing 100, so his car will have an 8% higher reading when he goes to change it.