Speedo Error R32

[Oneofthegreats]

Just to shed some light on this.

ADR's state that speedometer's are aloud a 10% decrepency but only if they read faster, not slower.

You can try your luck with VW, but if it meet's the standard's, then it's really up to them if they want to pursue it further.

I even had a copper tell me my business & said that his car is more accurate than my car cause his car was only 6 month's old & my car was 32 year's old, even though mine was calibrated 100%

Try telling him about ADR's & his speedo is out. He'll give you a ticket!

[Logzy]

It seems that some cars are affected and others are not, my speedo and odometer appear to be correct after the change and I've just done 1500km and the odometer appears to be correct after the trip. I'll do some more testing but at this stage it appears to correct.

As far as I can see it's only some US models that have this problem.

How did you verify that the odometer is correct ?

[Maverick]

How did you verify that the odometer is correct ?

GPS and distance to destination. You can also use the mile(km) markers on highways.

I wasn't specifically checking the odometer but everything looked right. I'll do some more testing.

[The_Hawk]

Police actually do (or at least used to) have their speedo's recalibrated regularily.

[mrx]

It seems that some cars are affected and others are not, my speedo and odometer appear to be correct after the change and I've just done 1500km and the odometer appears to be correct after the trip. I'll do some more testing but at this stage it appears to correct.

As far as I can see it's only some US models that have this problem.

I have tried changing the last number of the coding from 3 to 7, but it didn't appear to do anything, the speed on the climate control readout was still showing the same offset from the speedo as before. I don't have a GPS, so I don't know whether I'm really going faster or not.

[gareth_oau]

dont get too anal about speedo accuracy. wear on yr tyres from new to old will affect speedo accuracy by up to 3kph

[Maverick]

How did you verify that the odometer is correct ?

I checked it this morning on a 10.1km (GPS calculation of distance to work). Starting KM's were 152.3 and ending KM's were 162.2. That to me is pretty accurate as it was before, 9.9kms which is almost exactly 2% under which matches up with my canbus findings and those of others who have checked their odometer.

At this stage it seems to be accurate but I'll do some more testing to see and check my travel logs of my trip last week.

[bazzle]

dont get too anal about speedo accuracy. wear on yr tyres from new to old will affect speedo accuracy by up to 3kph

3kph when worn is ok..

That now means I will be 10kph out at 100ks later down the track. Yes I will remain anal.
I didnt purchase a vehicle to have to mentally work out the correct speed all the time.
Its my choice what speed I do, but I want it to be accurate.

Bazzle

[gareth_oau]

3kph when worn is ok..

That now means I will be 10kph out at 100ks later down the track. Yes I will remain anal.
I didnt purchase a vehicle to have to mentally work out the correct speed all the time.
Its my choice what speed I do, but I want it to be accurate.

Bazzle

My apologies Bazzle, no offence intended by my choice of term 'anal'. I should have used 'passionate', as we all are.

what i was indicating is that even if you got yr speedo spot on, it will still vary from day to day according to yr tyre wear.

Another way to compensate for yr speedo reading low is to put on slightly larger tyres

this webpage show how (new) widths and profiles affect speedo accuracy

http://www.miata.net/garage/tirecalc.html

and of course, a worn tyre might have an overall reduced diameter of around 15-20mm vs new

[Maverick]

My apologies Bazzle, no offence intended by my choice of term 'anal'. I should have used 'passionate', as we all are.

what i was indicating is that even if you got yr speedo spot on, it will still vary from day to day according to yr tyre wear.

Another way to compensate for yr speedo reading low is to put on slightly larger tyres

Which reduces the choice of tyre, decreases handling AND increases your odometer by ~10% over real mileage if you want the speedometer accurate.

And the Speedometer won't vary from day to day, it will vary over time with tyre wear like anything but you will go from being 2kph out to maybe 4kph out at 100kph whereas the current setup will be from 8kph to 10kph.

[bazzle]

No worries Gareth. I have been in the auto field for the last 40 years of my 55 year life and am familiar with tyre wear error , tyre sizing etc.
I wont be straying away from the 225/40/18s as fitted.

Can any one suggest a source in Eastern suburbs of Melbourne who can (or has) the Vag com etc to see if we can play with this?

Showed the USA TSB to dealer but service chap was not really interested.

Ta Bazzle

[Maverick]

I've conducted some further testing and on a trip of 32.5km (according to the GPS) I covered 32.7km according to the GPS (this included some frequent lane changes on my behalf) which is pretty spot on.

[The_Hawk]

For Reference:

The 205/45R16 on my Mk3, assuming the speedo is 100% accurate will read the following speeds at a REAL 100km/h as the tyre wears XXmm into it's tread, in short as you wear the tyre it becomes smaller so you have to spin it faster to cover the same difference. (that is for you to be travelling at 100km/h the speed would have to read these speeds)

New	100
1	100.3
2	100.7
3	101.0
4	101.4
5	101.7
6	102.1
7	102.4
8	102.8
9	103.1
10	103.5

And with the standard 225/40R18's available on the Mk5

New	100
1	100.3
2	100.6
3	101.0
4	101.3
5	101.6
6	101.9
7	102.2
8	102.6
9	102.9
10	103.2

Basically, the bigger the wheel the less difference wear will make.

But how much tread do you REALLY have to wear? I have allowed for up to 10mm in these calculations, but I'm not sure how much is in a normal tyre (or how far you let yours go).


But back to the point of all this, tyre wear as an excuse is a total farce, like I said the wheel gets smaller meaning you are covering LESS distace for a given number of RPM's of the wheel, so your speedo will say you are going faster than you really are and will only get worse as your tyres wear more. In short, even if the speedo was 100% accurate with brand new tyres it would NEVER read faster that you were actually travelling.

Just to be thorough, lets look at the standard option wheels (which is all VW really have to worry about). Let's assume that you calibrate the speedo to the largest wheel available (ie the one that will have the lowest RPM @ 100kmh), that way if you put a smaller wheel on the car the WORST that will happen is the speedo will say your going faster than you really are.

	Diameter	Circ	Rev/km	Speedo @100
195/65R15	634	1991.8	502.1	100.5
205/55R16	632	1985.5	503.7	100.8
225/45R17	634	1991.8	502.1	100.5
225/40R18	637	2001.2	499.7	100.0

Now looky there, there is bugger all difference with the different wheel options and remember that as the tyre wears you will actually start going slower for an indicated speed... so where exactly is the justification for a 10% discrepancy again?

[gareth_oau]

good technical analysis there Hawk!!

It shows that wheel/tyre options, if done correctly, dont really affect the accuracy of yr speedo.

My earlier comment was to suggest that if a speedo is out (and if VW arent willing to address it) then you could put an out of spec tyre (e.g. larger width, without lowering profile) to offset the lower reading of the inaccurate speedo.

Of course an easier fix would just be to re-calibrate yr mind to realise the speedo is slow and you can do 5-10k's more than indicated, without being nabbed

My understanding is that tyres typically have 10mm of treaddepth, so at the end of the day, yve reduced yr rolling diameter by 20mm overall

(I have had a tyre down to the steel band at one stage (when I was a bit hardup), so perhaps even more 'depth' then!!) (handling was really good too)

[The_Hawk]

My understanding is that tyres typically have 10mm of treaddepth, so at the end of the day, yve reduced yr rolling diameter by 20mm overall

My calculations of tread depth take into account the total reduction, so even with a 20mm reduction it still makes only up to 3.5km/h over reading difference.

But yeah, it's always nice to "speed" a little