[Guide] [T6_modified] T6 Speedo Adjustment with VCDS

[mmi]

Good. Now it's start to be exciting. You should change your coding so we can see how wheel circumference value changes.

The current wheel circumference 2111 mm implies wheel size of 215/60-17. Compared with that your wheel (235/65-17) has presumably wheel circumference 2247 mm (or it has to be coded like that).

So we need to find coding which gives close that wheel circumference.

My guess is coding "03 Distance impulse number 3..." will give wheel circumference value of 2252 mm. That would make your odometer read 6,7% more than now, and your speedo 6,7% EDIT: also more than now (overreads: if now 100, will be 107).

Change "Bit 0-3" to the above. Click "Exit", and click "Do it".

Then read the new values for "K-number IDE00842" and "Wheel circ. IDE00845" please.


The K-number (currently 22740) is number of pulses from ABS/wheel sensor for odometer to count 1000 meters. It's 48 pulses/wheel revolution.

 

[Glenn Board]

Thanks, will do tonight, so are you saying that we wont change the K number?

 

[mmi]

Thanks, will do tonight, so are you saying that we wont change the K number?

Actually we can change only the coding. The coding change will then reflect into measurement values "K-number IDE00842" and "Wheel circ. IDE00845".

So there are two different things (on different screens) (1)-coding that changes things, and (2)-measurement values which we can't directly change, rather they show us the effect of our coding change.

After the coding change I'm expecting to see in measurement values K-number to be 21312, if wheel circum. is 2252 mm.

 

[Glenn Board]

so is the circumference of my tyres not 2314?

 

[mmi]

so is the circumference of my tyres not 2314?

View attachment 25395

I know what you are saying. Unfortunately different calculators give different values. Did you check what you get for 215/60-17, which VW has coded as 2111 mm. I'm afraid it will show about 2166 mm.

Targeting to value 2247 mm (from another calculator which seems to match VW idea) with your new tyres we only make your odometer show same kilometres/miles as your van with 215/60-17 tyres with current coding.

Anyways, unfortunately this is a kind of trial and error procedure because only few preselected codings are available.

Hope this clarifies a bit. Anyways, thanks for your interest.

 

[Glenn Board]

Great, will work on your suggestions

 

[mmi]

Oops. Got confused last night
Should have been:
My guess is coding "03 Distance impulse number 3..." will give wheel circumference value of 2252 mm. That would make your odometer read 6,7% more than now, and your speedo also 6,7% more than now (overreads: if now 100, will be 107).

 

[Glenn Board]

Hi, went for option 3, doing a long run early next week, so will be good to test it, speedo now overriding at 100kph it ranges on gps between 74.6 and 76, so all looking a lot better thank you, I really appreciated your help on this, thank you.

 

[Adrian72]

Afternoon,

Is there anyone in the manchester area who would be willing to do this for me? Mine has got 275/45 r20's on and my speedo is under-reading and it is annoying to say the least.

I have no qualms paying for this.

Thanks
Adrian

 

[dennismo]

Hi there. I've just been reading this thread - extremely helpful. I'm planning to change the wheels on my Edition from the standard 235/55 R17 to 275/40 R20... From reading this thread, am I right that the following will happen:
- The speedo will under-read by approximately 5%
- Therefore, the Odometer will also under-read by the same amount?
- Other on board computer functions that are calculated from this (e.g. MPG) will equally show 5% lower than they actually are?

@Shredder helpfully commented that in reality, he didn't need to change this... but if I find that it's 5% out, do I simply need to find someone who can change this using the VCDS?

Does anyone else have experience of changing from 17" to 20" wheels and what difference it has / hasn't made?

Thanks so much in advance!

 

[mmi]

Hi there. I've just been reading this thread - extremely helpful. I'm planning to change the wheels on my Edition from the standard 235/55 R17 to 275/40 R20... From reading this thread, am I right that the following will happen:
- The speedo will under-read by approximately 5%
- Therefore, the Odometer will also under-read by the same amount?
- Other on board computer functions that are calculated from this (e.g. MPG) will equally show 5% lower than they actually are?

@Shredder helpfully commented that in reality, he didn't need to change this... but if I find that it's 5% out, do I simply need to find someone who can change this using the VCDS?

Does anyone else have experience of changing from 17" to 20" wheels and what difference it has / hasn't made?

Thanks so much in advance!

Yes, yes, yes. True, the speedo will read approximately 5% less than with factory wheels. And as you stated also the other figures will be the same 5% less. Obviously the consequence of the odometer accumulating less miles will result seemingly worse fuel consumption figures.

True, @Shredder has his speedo now reading correct as speedo was slightly over-reading with factory wheels. The "loss" now being that the van accumulates less miles into odometer and thus is showing poorer fuel economy . I would expect your results to be very close to his as the calculated correction is the same.

And, yes, it’s quite simple task with a VCDS.

 

[dennismo]

Very helpful! Thanks @mmi . I'll wait until the wheels are changed, measure with an app, and then decide if to get it changed on the VCDS. If under reading - would you recommend getting it changed? If so - who do I ask to do it for me? (@Shredder do you reckon Leighton Vans would be able to do it - since they're fitting the wheels?)

Cheers

 

[Shredder]

@dennismo I actually don't know if Leighton do VCDS coding, I've never asked. I wouldn't be surprised if they can, or use 'their' VW dealer to do it as people regularly ask for coding customisations to do with, needle sweep, folding mirrors, lock on drive away etc etc.

As you saw from the development of this thread between myself and @mmi ... the 20" rims on mine basically 'corrected' the speedo which was manufactured and fitted as under-reading in connection with some EU regulation or other. Therefore, I obviously didn't bother with a coding change.

The Odometer under-reading isn't really a problem IMO. Who will pull you up when you come to sell if you have a great service history file. So many people run 20"'s for their van's life anyway. As for MPG, you can't make it drastically better, so knowing what it is isn't that helpful. You pays your money

 

[mmi]

Very helpful! Thanks @mmi . I'll wait until the wheels are changed, measure with an app, and then decide if to get it changed on the VCDS. If under reading - would you recommend getting it changed? If so - who do I ask to do it for me?

Thanks. I would say it is just a matter of personal preference (not now taking into account any national regulations how the speedo must read). Personally I prefer calibrated display (speedo) but definitely not under-read.

Slightly off topic but as members interested in speedo accuracy are here I’m using the opportunity to ask if you have on your mph-speedos the same slight offset between digital readout and “traditional analog” speed display? See the picture below which was taken at steady speed using cruise control showing the needle to be slightly above "110" mark. This is consistent on all T6's I have driven and also on all decent speeds.

Even though it might seem to be a parallax error in the picture (because of the shadows), it is actually the way I see it on driver’s seat.

 

[Pauly]

Mine is the same, the needle often appears a fraction higher than the digital readout

 

[andys]

@dennismo I actually don't know if Leighton do VCDS coding, I've never asked. I wouldn't be surprised if they can, or use 'their' VW dealer to do it as people regularly ask for coding customisations to do with, needle sweep, folding mirrors, lock on drive away etc etc.

As you saw from the development of this thread between myself and @mmi ... the 20" rims on mine basically 'corrected' the speedo which was manufactured and fitted as under-reading in connection with some EU regulation or other. Therefore, I obviously didn't bother with a coding change.

The Odometer under-reading isn't really a problem IMO. Who will pull you up when you come to sell if you have a great service history file. So many people run 20"'s for their van's life anyway. As for MPG, you can't make it drastically better, so knowing what it is isn't that helpful. You pays your money

The EU regulation in question (adopted into UK law) only allows for an OVER-reading and no under-reading at all.

 

[dennismo]

I feel like I’m finally getting my head around this...how do I go about asking someone to make this adjustment? I’m guessing I can’t simply walk into a VW van centre and ask them to help?

 

[Shredder]

I feel like I’m finally getting my head around this...how do I go about asking someone to make this adjustment? I’m guessing I can’t simply walk into a VW van centre and ask them to help?

So how far out from actual is your Speedo now ?? Quite curious, as you are going for the same set up as me and my Speedo reads pretty much spot on because the new wheel and tyre change took up the built 'under-reading' at the point of manufacture.

 

[dennismo]

@Shredder - Yet to establish the inaccuracy of Speedo, but even if the 5% makes the speedo accurate, what I understand from @mmi is that the odometer will under read by 5%. Research has shown me that, even if speedo's are designed to over-read, odometers are designed to be exactly accurate. Odometer under-reading is an issue for me, as I need to accurately track business mileage! I would prefer to adjust the VCDS, and end up with a speedo that over-reads, but have an odometer that is accurate... just personal preference for my needs I guess... SO if anyone has ideas of who to go to for this adjustment, that would be super!

 

[Shredder]

I get your point, if it's not the Speedo that's your highest priority. As you say, depends on what you use your van for. For me, not getting caught speeding in Europe or the UK (with our whacky van/MPV speeding rules) is the number one priority. For business mileage, I use the Google Maps mileage per trip for claims. HMRC would probably use Google as well if you were being investigated by them