# How accurate is the Phaeton speedometer?



## PC Dave (Nov 29, 2001)

On the highway, I tend to set my cruise control at a "safe" margin over the posted limit to maximize average speed without attracting unwanted (and expensive) attention. If the speedo reads high (e.g. speedo says 60, I'm doing 55) then I'd like to kick the set speed up a notch; on the other hand if it's accurate I don't want to take the risk. I was clocked on our local public radar sign at 27 when my speedo said 30 - I'm not about to test there (in a 25 zone) to see if the inaccuracy is a percentage or absolute spread at 70







.
In my experience, auto manufacturers tend to build a consistent inaccuracy into all their speedos (BMW = 10%, Mercedes = no inaccuracy). Does anybody have experience with higher speeds in the Phaeton?


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## agnos (Jul 20, 2004)

*Re: How accurate is the Phaeton speedometer? (PC Dave)*

Not sure about the Phaeton in particular, but I recall reading an article in the LA times a couple of years back that stated that by law, German cars have a slightly greater deviation than American cars - i.e. the speed in the speedometer is usually a bit higher than actual speed. If I recall correctly, it is a saferty margin or something like that. However, the article also went on to state that although the legal requirement applied to the speedometer, it did not apply to the on board computer (which is used to calculate trip distance, fuel consumption, etc), so looking at the instantaneous speed in the computer would give a more accurate picture.


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## 05bntly (Jan 3, 2005)

If the Phaeton speedo is the same as the Bentley Continental GT, and I'm pretty sure it is, then is it off by 10%. My Bentley is off that much; the dealership has confirmed it. The factory says "just live with it". They have no interest or intention of trying to make it accurate.
You can read more in my posts in the Bentley section.


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (agnos)*

The legal requirement in Europe (it's a EC regulation, not just a German one anymore) is that the speedometer may not, ever, indicate a speed that is lower than the speed that the car is actually traveling at. 
My experience with VW's in Europe - I have a Golf as a company car in Switzerland - is that the speedometer is usually very accurate, at the most it reads 1% or 2% high. On my Golf, this is a constant linear deviation, as a percentage, it is unchanged at all speeds. When my Swiss dealer puts the snow tires on the Golf in the winter, they make a small correction to the speedometer with the VAS 5052 scan tool, to correct for the larger diameter of the snow tires.
My North American Golfs and Jettas always had much larger errors in the speedometer, typically they would read about 5% to 7% higher than actual speed, again, on a linear basis. This I know because I used a Garmin GPSR in all my Golfs.
I do know that the Phaeton offers the ability to correct (calibrate) the speedometer as needed, again using a VAS 5051, 5052, or other diagnostic scan tool such as a VAG-COM. I have not bothered yet to check the Phaeton speedometer for accuracy. I'll check into it later this week and let you know what I find.
Michael


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## spockcat (Jun 5, 2003)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

On the Touareg, the speedometer indicate about 3 mph faster than you are actually travelling at 60 mph. However, if you check this speed against the indicated average speed in the MFI (say by driving an indicated 60 mph on cruise control over a few miles), the MFI is accurate and will read 57 mph. This has been checked by GPS and many owners report the same or very similar results.
So it seems that in North America at least, VW makes the speedometers read faster than actual speed. 
Get a GPS unit or drive 60 mph over a measured mile with a stop watch in hand and check your own speedo.


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (spockcat)*

Thanks, Jim, much appreciated.
For the info of all, the Phaeton instrument cluster is almost identical to the Touareg instrument cluster, although that does not guarantee that the behavior of the two will be identical.
Michael


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## av_audi (Apr 5, 2001)

*Re: How accurate is the Phaeton speedometer? (spockcat)*


_Quote, originally posted by *spockcat* »_On the Touareg, the speedometer indicate about 3 mph faster than you are actually travelling at 60 mph. However, if you check this speed against the indicated average speed in the MFI (say by driving an indicated 60 mph on cruise control over a few miles), the MFI is accurate and will read 57 mph. .

That is also exactly my expeirence with the Passat, and it seems to be valid for most VW models sold in the U.S. The check with the trip computer is very easy and straightforward.


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## AusSalzburg (Nov 4, 2004)

*Re: How accurate is the Phaeton speedometer? (av_audi)*

My experience in this subject has been that the vehicle speed signal to the instrument cluster is correct. The computer takes the speed signal and splits it. The odometer is correct. The indicated speed is purposely set a little higher. You can see this IN signal in kilometers with the 5052 but the "Indicated Speedo" speed is higher, usually by 5-7%. 
With a GPS or just simply time how long it takes to travel between mile or Kilometer markers on the side of the highway. At A TRUE 70 MPH (113KPH) it should take 51 seconds to travel between each marker. However on our cars it normaly takes about 55 seconds which is realy about 65 MPH. When looking at the IN signal on the cluster with the 5052 you'll see 105 KPH when traveling at 70 MPH indicated. 105 KPH or 65 MPH is your true speed. 
We all cant drive around with 5052's or RossTech software to see our hidden digital TRUE speed. Just remember that for every 20 MPH INDICATED you LOOSE about one (1) MPH.
In my world the speed limit is 130 KPH. I set the cruise at 150-160 knowing that actual speed is 139-148 KPH. Our policemen don't look at you until you are traveling over 150.
PanEuropean, please find the login password in the instrument cluster to change the "Adaption" or adjustment of the Indicated speed. I've done this adjustment before about 4 years ago but lost the code. I also remember when I changed the adaption, it changed the accuracy of the odometer. But I still want to play with this feature one more time.
Thanks,
Werner


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## av_audi (Apr 5, 2001)

I have never had to use any such elaborate procedures. Either the short term or the long term memory of the "trip computer" (whatever it is called on the Phaeton) can be reset anytime. So when I am cruising at a constant speed, I just reset the short term memory, and within seconds, I have the average ODO-based speed since the reset.


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (AusSalzburg)*

Werner, what you say is correct, but VW introduces a different "error" into the North American products. Before I bought the Phaeton, I had two identical 2002 Golfs - one in Canada, one in Zürich. At that time, I was doing GPS testing for Garmin, so I always had a top of the line GPS in the car.
The Swiss car had about a 3% error (read 3% high), but the dealer corrected that to zero when I requested they do so. The Canadian one had a 7% error, and the dealer told me that they would investigate correcting it if I wanted them to do so, but they had never been asked to correct one in the past - so the procedure would be new for them.
There are huge differences between the products sold on either side of the ocean, even if they come out of the same plant.
Michael


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## Highline (Mar 13, 2003)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*


_Quote, originally posted by *PanEuropean* »_
There are huge differences between the products sold on either side of the ocean, even if they come out of the same plant.
Michael

Maybe that's one of the reasons for what it seams like higher number of problems on European cars sold in North America.








VW blamed the window regulator's failure on a specific chemical componet used only on North American car washes, is possible that maybe there is a higher level of electro-magnetic pollution in NA or simply a different and not fully test-proofed software packagge?


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

Here's the result of my tests today, conducted with a 12 channel GPS with differential correction, on an airport runway, with the Phaeton stabilized and the cruise control on:
81 km/h indicated on speedometer = 76.5 km/h actual (measured) speed
100 km/h indicated = 94 km/h actual
120 km/h indicated = 113 km/h actual
It looks to me like there is a pretty constant error in the speedometer, whereby it indicates that the vehicle is moving about 7% faster than it actually is moving. That is exactly the same amount of indication error I experienced on my 2002 Golf
I will check with my 'Phaeton enthusiast' friends and see if there is a way we can correct this.
Michael


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## AusSalzburg (Nov 4, 2004)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

Hi PanEuro,
Did you happen to have your Rosstech hooked up at the same time to verify that the measuring blocks in kilometers match the GPS?
Werner


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (AusSalzburg)*

The VAG-COM? No, I didn't, but that sounds like a good idea. When I get a chance, I will try that.
Michael


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## VWinA (Oct 20, 1999)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

My father used to have the 2 most prestigious VW's sold in NA.
The first was an 85 Jetta GL with all options (before the carat arrived). And the second one was a 91 Passat GL, Burgundy with tan leather and all options again...
Lame intro but true nonetheless








Unfortunatly, that feat can't be repeated.
In the Passat, the speedometer needle indicates +- 10% more. Setting the cruise at precicely 100Km/h and reseting the mfa, you could then see the average speed being around 93Km/h. That average speed is calculated from the same source as the odometer, wich is _perfectly_ accurate.


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## theskippur (Jun 26, 2000)

*Re: How accurate is the Phaeton speedometer? (VWinA)*

THIS MUST BE WHY EVERONE IN SEATTLE DRIVES SO SLOW!! It's because everyone in Seattle drives a VW.


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (AusSalzburg)*

I did the Phaeton speedometer test again, this time using a diagnostic scan tool to read the speed calculated by the vehicle speed sensor (this shows up in quite a few data measuring blocks, I used the speed input to the ABS system via the powertrain controller area network bus).
The speed being reported to the ABS system and the speed being calculated by the (external) differential GPS system were within a quarter of a percent of each other - this was actually the limit of how precisely I could measure them. I logged both values, and compared them later on a computer.
It appears that the error is in the value displayed by the needle on the face of the speedometer. I will check with our friends and see if this can be adjusted.
Michael


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## AusSalzburg (Nov 4, 2004)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

Any luck with the secret code?
Happy weekend everybody.
Werner


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (AusSalzburg)*

We're not even at the stage of knowing where to make the adaptation (calibration) yet, let alone having to figure out the secret code to do it.
Michael


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## AusSalzburg (Nov 4, 2004)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

The address word is 17 for the cluster. From a few years ago I rember going into adaption 10 and changing something. 
It was something like Log-in 11 once in the cluster, then enter 12233, then adaption 10. Once in there someting was changed. Changing the speedo to read higher was easy. I just can't remember anymore. I do remember it changing the accuracy of the odometer in a negative way.


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (AusSalzburg)*

Ah-ha, most interesting. Thank you for the help with that. What I am still trying to figure out is how to correct the indication of the speedometer needle, but without changing the setting for tire circumference. The digital speed readings - as passed, for example, from the ZAB to the ABS unit - are highly accurate, within 0.25% of actual speed. So, the problem is only that the needle reads high, not the speed sensing system in general.
Michael


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## rmg2 (Jan 23, 2004)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

Just curious does the odometer read correctly? It seems if the odometer is tied to the speedo calibration then a higher reading (+) on the speedo would mean higher odometer mileage thus those of us who lease would be getting fewer miles than we're allowed.
Or am I just confused?


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (rmg2)*

Everything is correct, with the sole exception of the position of the needle on the face of the speedometer. So no worries about lease mileage, stuff like that.


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## acolakoglu (Apr 6, 2005)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

My 2002 Passat constantly reads +2-3 mph more (@ around 70 mph)
and the new 
2005 Touareg reads +4 mph more than (@ around 80 mph)
the actual speed. This is not acceptable. 
I talked to the VW service, they told me there is no way to fix it and advised to call customer service. I will keep you posted.


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## acolakoglu (Apr 6, 2005)

*Re: How accurate is the Phaeton speedometer? (acolakoglu)*

I found a very interesting article and I believe this is the answer to the problem:
http://www.caranddriver.com/ar...ber=1
Do not forget to read the 2nd page.
I will not call the customer service after reading it. As all of you guys have agreed and the article suggested, the trip computer and trhe speed warning are accurate but the speedometer is offffff!


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## AusSalzburg (Nov 4, 2004)

*Re: How accurate is the Phaeton speedometer? (acolakoglu)*

Hello again Mr. Moore,
I know you are a busy pilot and some how you find time to write so much technical info here in Vortex. I don't know how you do this and balance being a husband also. You are very valuable to VW of America. 
You are kind-of like the Phaeton Customer Service advocate and the Phaeton Tech support for VW of America. You should get a job there.
Anyway, I'm just curious if you have figured out how to adapt the speedo? No big rush on this, just curious.
Thanks,
Werner.


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (AusSalzburg)*

Hi Werner:
Thanks for your kind words. I have not figured out how to do it yet, but I will be in Dresden in two weeks for the Phaeton treffen there, and I will ask if there is a way to correct things. Right now I am travelling and have very limited internet access.
Michael


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (AusSalzburg)*

Werner:
Will you be in Salzburg during the period May 25 to 27? If so, I will try to swing by and perhaps we can have lunch or dinner. Let me know.
Michael


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## 8secondquarters (Apr 7, 2005)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

The answer appears to be very accurate
i use an extremely accurate gps based speed camera detector in the car which has a digital speed read out
http://i6.photobucket.com/albu...6.jpg
















every other car i have had this equipment in showed 5 - 7 mph fast


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (8secondquarters)*

Steve:
Thanks *VERY *much for making the post above, and sharing your observations. What you have done is remarkable - you have confirmed that there is a way to calibrate the needle on the gauge so that the needle presents accurate information.
Before you made your post, we all knew that it was possible to make an adjustment to the vehicle to compensate for an increase (or decrease) in tire circumference, and this would affect the entire speed measurement system (meaning, speed shown on trip computer, speed used by navigation system when in DR mode, speed used by ABS system, and the indication of the needle on the speedometer face). Your pictures suggest that there should be a way to adjust the needle indication, to get rid of needle error *without *affecting any of the other speed readings.
There is only one thing I need to double-check with you - are you using standard tires and rims on your Phaeton? By this I mean is the circumference of your tires today the same as it was when the car left the factory?
Let us know.
Michael


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## carrerarsr (Jan 5, 2005)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*

My V10 in Germany shows 270 km/h on the Autobahn. The avg Speed when resetting the computer then is 258 km/h. GPS shows usually a 10 km/h difference.


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (carrerarsr)*

Hi Frank:
Thanks for that info. Since I made the post above, in reference to Steve's information, I have discovered that Steve has aftermarket tires on his Phaeton. This means that it is possible that he has a larger wheel circumference than what was originally supplied on his car - and as a result, the speedometer is now reading correctly, rather than a few percent high. We'll have to wait for confirmation of this by Steve.
Michael
*Steve's Wheels and Tires*


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## viscount (Jan 2, 2005)

*Re: How accurate is the Phaeton speedometer? (carrerarsr)*

i had it up to 134 mph tonight on the speedometer and didn't feel the limiter setting in







so @ +7% that means only 126 mph.. i didn't have a chance to keep going








Ed.


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## 8secondquarters (Apr 7, 2005)

*Re: How accurate is the Phaeton speedometer? (viscount)*

Hi Micheal
The car was equipped from new with 17 inch rims and 235/55/17 tyres
and is now running 19 inch rims with 245/45/19 tyres
the 17's gave a diameter of 27.18 inches or 690mm
19's give a diameter of 27.68 or 703mm
a difference of 1.88 % or somewhere around the difference between new and worn out tyres
Steve


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## 8secondquarters (Apr 7, 2005)

*Re: How accurate is the Phaeton speedometer? (8secondquarters)*

usefull link to a tyre size calculator
http://www.tyresave.co.uk/tyresize.html


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## Paldi (Sep 4, 2004)

*Re: How accurate is the Phaeton speedometer? (8secondquarters)*


_Quote, originally posted by *8secondquarters* »_Hi Micheal
The car was equipped from new with 17 inch rims and 235/55/17 tyres
and is now running 19 inch rims with 245/45/19 tyres
the 17's gave a diameter of 27.18 inches or 690mm
19's give a diameter of 27.68 or 703mm
Steve

Now that's interesting. You're first to go with larger diameter tires than stock.
You chose the 245-45-19 tire for your new wheels. That tire is 27.68 inches tall.
However they are not as wide as the stock tires on the 18" wheels: 255-45-18 at only 27.04 inches tall. You went taller, but narrower.
I wonder if you can't go 10mm wider to the same width as the 18's setup at 255mm?
Using a 255-45-19 tire you would have the stock width used on the 18" wheel setup but the tires are 28.04 inches tall! A full inch taller than the 18's but only .36 inch taller than your 19" wheel setup. Will these fit? They are 3.6% taller than the 18 inch tires. The speedo error has been reported to be 3 - 7 percent.
I anticipate the speedo error will be reduced by the taller tire - perhaps eliminated entirely. (sorry - pun)











_Modified by Paldi at 10:13 AM 5-14-2005_


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## PanEuropean (Nov 3, 2001)

*Re: How accurate is the Phaeton speedometer? (PC Dave)*


_Quote, originally posted by *PC Dave* »_On the highway, I tend to set my cruise control at a "safe" margin over the posted limit to maximize average speed without attracting unwanted (and expensive) attention. If the speedo reads high (e.g. speedo says 60, I'm doing 55) then I'd like to kick the set speed up a notch; on the other hand if it's accurate I don't want to take the risk. I was clocked on our local public radar sign at 27 when my speedo said 30 - I'm not about to test there (in a 25 zone) to see if the inaccuracy is a percentage or absolute spread at 70







.
In my experience, auto manufacturers tend to build a consistent inaccuracy into all their speedos (BMW = 10%, Mercedes = no inaccuracy). Does anybody have experience with higher speeds in the Phaeton?

Hi Dave:
I asked the engineers in Dresden about this when I was at the GTG there last weekend. They told me that the speed measuring system in the Phaeton is deadly accurate - within about 0.25% accuracy - so far as the measurement that the Phaeton uses internally, for use by the ABS system, navigation system, and ESP system.
But - the explained that there is a deliberate error built into the needle on the speedometer, which causes the needle to read about 5% to 7% high. This is because the law in most countries - Germany and the United States, to name just two - requires that the display presented to the driver be calibrated in such a way that it will never, under any circumstances, read less than the actual speed of the vehicle. So, the engineers figure out what the largest possible tire size is that can 'reasonably' be fitted to the vehicle, and calibrate the needle so that it displays the exact correct speed with that oversized tire installed.
The effect of this is that, as you pointed out, the speedometer reads high when 'normal' size tires are fitted.
There is some possibility that this problem will be addressed in the future, when GPS systems become 'standard equipment' on cars. If all cars in a product line have GPS as standard fitment, this allows the engineers to set the car up so that whenever it is being driven in a straight line at a steady speed for about a mile or so, it will 'self-calibrate' the speedometer needle to the GPS measured groundspeed. If this can be done, then there is no need to build a pad (error) into the speed indicated on the face of the speedometer. The current Phaeton (2002 - 2006) does not have GPS as standard equipment - it is optional in markets outside of NAR. If the next model (2007 facelift and on) incorporates GPS as standard equipment, then maybe we might see this fix for the problem.
Michael


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## Gobuster (May 19, 2005)

After reading these posts, I was curious to see if another German marque, namely BMW also built in a "fudge factor" with regard to speed readings. So, today, with a long road trip ahead, I dusted off my old Garmin Street Pilot and did some testing with my E39 540i. 
Using cruise control to stabilize the speed for at least a mile, I observed the following:
Indicated 60, 70 and 80 were GPS 58, 68 and 78. 
given that the GPS does not read in tenths, I assume that any real speed between 57.6 and 58.4 will read 58 and so on, I conclude that the error on this car runs in the range of 2 to 4 percent fast. I'm running stock 225/55 16 tires about half worn, so, with new tires the speedo should be about dead on!
When I get my Phaeton (soon I hope) I'll try a test on new tires to see if my error is the same 5-7% others report. I'll use the same GPS unit to standardize the results.
My trip turned out to be a breeze, the V8 Bimmer ate up the road! Some interesting trip stats:
Total miles 296
Driving average 77.2 mph
Fuel consumption 24.1 mpg
Max. speed for trip 112.9 (I nailed it to go around a few trucks, had no idea I went quite that fast!). This stat does read in tenths, but I can't easily use it for calibration since it is peak only.
Can't wait to try this run in the Phaeton, which should be even more serene and stable.
Rob.


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## rmg2 (Jan 23, 2004)

*Re: How accurate is the Phaeton speedometer? (PanEuropean)*


_Quote, originally posted by *PanEuropean* »_
Hi Dave:
But - the explained that there is a deliberate error built into the needle on the speedometer, which causes the needle to read about 5% to 7% high. This is because the law in most countries - Germany and the United States, to name just two - requires that the display presented to the driver be calibrated in such a way that it will never, under any circumstances, read less than the actual speed of the vehicle. So, the engineers figure out what the largest possible tire size is that can 'reasonably' be fitted to the vehicle, and calibrate the needle so that it displays the exact correct speed with that oversized tire installed.

Hi Michael,
The $65K question is . . . what is the larget tire size that can fit on a Phaeton?


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## PanEuropean (Nov 3, 2001)

*Re: (Gobuster)*

Hi Rob:
Interesting info about your GPS testing. Your StreetPilot will read in tenths - you just need to go to a different screen to see the tenths. What screen you go to depends on whether you have an original SP, SP III, or SP 26xx series. I have them all (I beta-test for Garmin)- let me know if you have any questions.
Respecting SP use in a Phaeton, you will need an external antenna. The solar reflecting film that is built into the glass totally blocks the satellite signals. On the occasions when I am doing Garmin testing in my Phaeton, I just stick the external antenna on the roof, via the sliding hole in the roof. If someone wanted to mount an external antenna permanently, under the front fender (which is plastic) would probably be a better place.
*Rick:* I don't know, but mathematics suggest it would be a tire with a 7% greater circumference than what comes standard on the vehicle.
Michael


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## Gobuster (May 19, 2005)

Hi Michael,
Mine is an original SP, I've had it since '99 and it's guided me faithfully for many a mile, and even a kilometer or so in Europe! I was using the speed readout on the trip recorder screen and did not check to see if it reads tenths on the speed shown on the map screen. I've been thinking of getting a new one but am undecided between the convenience of the ones with a hard disc or the lightness of the memory chip. Out of the Quest, c320/330 and 26xx series, I'm having a tough time deciding! I'm leaning towards the Quest because it's light and from what I've read, is an excellent performer. Which one is your personal favorite?
I thought the solar film glass was only in the W12 and that the V8 had the regular tinted glass, am I wrong? Does the solar glass have a "window" for a radar detector or do you have to go external there too? I think detectors are outlawed in Ontairo, but where I live, they can be a license saver!
Rob


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## PanEuropean (Nov 3, 2001)

*Re: (Gobuster)*

Hi Rob:
I'm not entirely sure what the deal is with solar reflecting glass on V8's. In fact, I am pretty confused about solar reflecting glass on W12's - David Cowan and I compared our cars a month or so ago, for sure we have different glass, but my build sticker says I have solar glass. PC had solar glass on her V8, so, it can be done. Someday I will get it all figured out.
Respecting the StreetPilot GPSR's, if you need big storage capacity for maps, then the SP 26xx series is the only way to go - it can hold up to 4 gigs of maps on a standard CF (flash memory card) that you can buy at a Wal-Mart. Because I do long distance motorcycle riding in Europe, and I don't want to have to be constantly reloading maps into the GPSR from my laptop, I prefer the SP 26xx. The Quest is a very good unit too, it has fixed, non-expandable memory inside it. If you don't often make really long (500 mile out or more) trips, or, if you normally travel with a laptop, then the Quest would be quite suitable. I am not familiar with the c320/330 series, so I can't comment on them. If you are a mariner, then the 296 would be worth looking at as well, although it is handicapped (for automotive use) by a 256 meg limitation on memory chip size.
It's kind of hard to say that one specific Garmin GPS is the best for a certain purpose. The models overlap quite a bit now, meaning, it is not uncommon to find two or more units that are fully suitable for a certain specified purpose.
Michael


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## AusSalzburg (Nov 4, 2004)

*Re: (PanEuropean)*

PanEuropean,
I found something on the Jetta A5 section. Here is a link to a website. Is this any help on coding the instrument cluster on the Phaeton?
http://en.openobd.org/vw/golf_1k.htm#17

This is the thread>>http://forums.vwvortex.com/zerothread?id=2039227
Werner


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## PanEuropean (Nov 3, 2001)

*Re: (AusSalzburg)*

Hi Werner:
That information is substantially the same as what I included when I wrote the VAG-COM label file for the Phaeton instrument cluster. I know the person who maintains the OpenOBD website, in fact, I had dinner with him in Dresden a few weeks ago. He posts here under the name 'Theresias'. There is a picture of he and I together at this URL: Glass Factory in Dresden invaded by Space Aliens.... There is a plain text explanation of how to code the Phaeton instrument cluster at this link: How to get rid of the seat belt warning message and chime. BTW, on the OpenOBD website, always use the German language pages, they are more complete.
Michael


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## Gobuster (May 19, 2005)

*Re: (PanEuropean)*

Finally had a chance to check the speedo error on my Phaeton, the result, approx. 5% fast. At a steady 80 on the clock the GPS read 76. At 80 on the GPS, the speedo was 84. The variance of approx. 4 mph was across the speed range 60-90 mph. Leads me to believe the car was designed to run on 255/50 18's, with them the speedo should be quite accurate!
Michael, the V8 does not have the heat absorbant glass, as my SP picked up the sats right away on its internal antenna. Still can't figure out how to get an instantaneous speed readout with tenths. The speed is displayed on the trip recorder page or the map page, both show whole numbers. Am I missing something in the setup? 
Rob


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## Paldi (Sep 4, 2004)

*Re: (Gobuster)*


_Quote, originally posted by *Gobuster* »_
Finally had a chance to check the speedo error on my Phaeton, the result, approx. 5% fast. At a steady 80 on the clock the GPS read 76. At 80 on the GPS, the speedo was 84. The variance of approx. 4 mph was across the speed range 60-90 mph. Leads me to believe the car was designed to run on 255/50 18's, with them the speedo should be quite accurate! 
Rob 

Ah yes, but will they fit? The spare tire well is already pretty tight for 255/45 18. The 255/50 18's might just push the envelope to the max. The 50's are about an inch larger in diameter. So are 255/45 19's if you care to go up an inch in the wheel size too...


_Modified by Paldi at 11:36 PM 6-27-2005_


----------



## Gobuster (May 19, 2005)

*Re: (Paldi)*

Fred,
Good point, if you kept the 45 spare as stock and put on 50's the 4 motion would be very unhappy if you had a flat and put on the spare! Guess you could stow a 50 spare flat and pump it up with a 12V compressor if you needed it








What do you think of these wheels, might show off those beautiful discs a bit better!
Rob


----------



## digifant_gli (May 14, 2004)

*Re: How accurate is the Phaeton speedometer? (8secondquarters)*

Not that you can even compare the 2, but my 1990 Jetta GLI always reads about 10% higher than my actual speed. My GPS confirmed. On a recent trip to the cottage, I set the cruise control to 120km/h. The speedometer in the car read 120 km/h on the nose, whereas the GPS said that I was doing about 110km/h...
I would assume that the GPS is more accurate than the car, as it is more modern technology.


----------



## Gobuster (May 19, 2005)

*Re: (Gobuster)*

The picture in my last post didn't work! It was supposed to show 5 spoke wheels but the copy from TireRack defaulted to stock! I'll try a photoshop later!
Rob


----------



## Paldi (Sep 4, 2004)

*Re: (Gobuster)*

Five spoke 18 inch wheels from the Audi A8 fit on the Phaeton. I test drove this one before I bought my Luna Blue V8.


















_Modified by Paldi at 11:24 PM 6-27-2005_


----------



## Paldi (Sep 4, 2004)

*Re: (Gobuster)*

Two sets of new Pirelli PZero Asimmetrico 255 50 ZR 18 102Y are f/s on ebay now. Pretty cheap at only $480.00/set of 4. Tires are 28" tall according to the tire size calculator. They look tempting.
http://cgi.ebay.com/ebaymotors...=WDVW

_Modified by Paldi at 3:58 PM 7-1-2005_


_Modified by Paldi at 9:58 AM 5-21-2006_


----------



## riccone (Nov 11, 2004)

*Re: (Paldi)*


_Quote, originally posted by *Paldi* »_Five spoke 18 inch wheels from the Audi A8 fit on the Phaeton. I test drove this one before I bought my Luna Blue V8.

















_Modified by Paldi at 11:24 PM 6-27-2005_
I think any wheel that fits an A8 will work on the V8 Phaeton as well.


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## Gobuster (May 19, 2005)

I was browsing the Tire Rack site and read the reviews on our Michelin OEM tires. In the reviews this tire finished last of 15 tires in the category! Makes me wonder how the car would perform on the #1 tire.
My Phaeton now has 1,000 miles and the ride continues to improve as the suspension settles in and I've got the tire pressures down to a reasonable level. This car really is a pleasure, it's going to be hard to keep the milage within lease allowance!
Rob


----------



## GripperDon (May 9, 2005)

Regarding Metallic film on the V8. I ran a test that has me believing the the V8 does have the metallic film. _It's an easy test and everyone can do it._ 
Simply turn on your cell phone. Hold it in one position steady! Roll the window up and down and note the difference in signal strength bars. Mine went from 3 bars driver window down to *NO BARS* window up!
Don 


_Modified by GripperDon at 12:13 AM 7-2-2005_


----------



## Gobuster (May 19, 2005)

*Re: (GripperDon)*

I haven't tried that test yet, but my cellphone works fine with windows up in my V8, as does radar detector and Garmin GPS used to check the speedo error. Doubt this would be the case if it had the heat reflecting glass! 
Rob


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## Kcmover (Jul 20, 2005)

*Speedo Calibraiton---how do they do this!*

How do I know if my speedo is properly calibrated. It seems that when I'm going 70 to 75 mph that cars are still zooming by me. Just wondering if my speedo is off. What is the best way to verify its operation. Is this something the dealer can do in house.


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## Gobuster (May 19, 2005)

*Re: Speedo Calibraiton---how do they do this! (Kcmover)*

The easiest way is to time the car between mile posts. It takes 48 seconds to do 1 mile at 75 mph. So, one day when traffic is light, set your cruise at 75 and time the miles. You can easily work out any percentage difference based on your results. Its best to time several miles then average the result to reduce any error due to the mile posts being slightly out.
An even easier way is to get hold of a portable GPS unit and compare the speed readout against the speedo in the car. GPS units provide quite accurate speed info. I calibraled my Phaeton this way and found the speedometer was reading 4-5% fast at 70-80 mph. I think the dealer can correct that error, but it doesn't bother me enough to make that worthwhile, I just subtract 4 mph from the reading and know how fast I'm going.
Hope this helps,
Rob


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibraiton---how do they do this! (Gobuster)*

4-5 mph is rather off a bit. I figured at most 3 mph. So in reality, I was only doing 124 mph on my way to work this morning. Hmmm.


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## Paldi (Sep 4, 2004)

*Re: Speedo Calibraiton---how do they do this! (Gobuster)*

I don't think the dealer can correct the speedo error. (I hope I'm wrong.) I believe the only thing you can do is increase the diameter of your tires. As we've discussed in numerous other threads, a one inch taller tire will eliminate much of the error.


----------



## Gobuster (May 19, 2005)

*Re: Speedo Calibraiton---how do they do this! (Paldi)*

Fred,
I finally pulled the trigger on a set of 255/50 18 Avon tires. If my calculations are correct, these should make the speedo accurate! I'm hoping to get wheels this week so I can drive to the Southern GTG on the new rubber. After I've got some experience with them, I'll post a full report.
Rob


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibraiton---how do they do this! (Gobuster)*

I can't wait to see that. I will do the same thing if you have good results. (of course when I need new tires).


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## Paldi (Sep 4, 2004)

*Re: Speedo Calibraiton---how do they do this! (Gobuster)*

Rob,
That's great news. If it fits, it will be a significant improvement in ride and appearance. http://****************.com/smile/emthup.gif 
Please check the fit of the spare tire well. That's the only thing that's holding me back.


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## car_guy (Aug 19, 2005)

*Re: Speedo Calibraiton---how do they do this! (Gobuster)*

Actually there's an easier way to check for the speedo error. I think this was written up on another thread, but I'll repeat it. Remember, I'm doing this from memory, so forgive me if I forget a step.
First display the 'Tripdata' on the infotainment screen. You can also display the average speed on the small screen between the tach and speedo. Find an empty stretch of highway and set your cruise control to any speed. Now what you want to do is Reset just the data for the current trip data. Your true speed will now be displayed as the average speed in both displays.
This works because, as I believe Michael has explained, the average speed is determined using the odometer (not the speedo), which is very accurate if you have the recommended wheels and tires. I have done this and found the speedo is 7% optimistic, which is the same as I believe Michael has found.


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibraiton---how do they do this! (Paldi)*

Fred, what would be wrong with just using the spare as is. You will hopefully be driving on it for only a short period of time if you get a flat. I wouldn't mess with the spare. I mean, it's better than a doughnut spare would be.


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibraiton---how do they do this! (car_guy)*

Thanks for that tip. I will get out today and try that. My office is next to the freeway and it wouldn't take me 15 minutes to do this.


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## Paldi (Sep 4, 2004)

*Re: Speedo Calibration---how do they do this! (dcowan699)*

Hi David,
I've had two flats in 5 months! I just want it to fit and I don't want to have to restrict my driving speed or distance whilst using the spare. In my business - real estate, I can't always drop everything to get a flat fixed. My trunk is full of signs and gear. 
I think, and this is just speculation on my part, that going any appreciable distance on a 1 inch shorter tire could do harm. http://****************.com/smile/emthdown.gif 


_Modified by Paldi at 12:38 PM 10-3-2005_


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibraiton---how do they do this! (Paldi)*

I see. I didn't realize you'd had two flats. I dread the day I have a flat.


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## PanEuropean (Nov 3, 2001)

*Re: Speedo Calibration---how do they do this! (Paldi)*


_Quote, originally posted by *Paldi* »_I think, and this is just speculation on my part, that going any appreciable distance on a 1 inch shorter tire could do harm.

It would certainly confuse the ABS and the traction control (anti-skid) system something horrible - because the car would interpret the rotational speed of a smaller wheel as indicating that wheelspin was taking place, because the smaller wheel would rotate faster than the other three.
Michael


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibraiton---how do they do this! (dcowan699)*


_Quote, originally posted by *dcowan699* »_Fred, what would be wrong with just using the spare as is. You will hopefully be driving on it for only a short period of time if you get a flat. I.

I feel stupid now!!


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## Gobuster (May 19, 2005)

*Re: Speedo Calibration---how do they do this! (PanEuropean)*

The rotational speed difference between 255/45 and 255/50 is about 3.7%. I think most traction control/ESP systems have some threshold before coming into play to allow for differences in rotational speed while the car is cornering. For example, a Phaeton in tight manouvering could easily turn a 60' diameter circle. Lets say the outer wheel is turning a 62.5' diameter and the inner 57.5' (given a 5' track). The difference in rotational speed would be in the order of 6%, yet ABS and ESP don't seem to be confused by this manouver. It would be interesting to find out what that allowance is. Michael, maybe your Dresden contacts could tell you. 
I doubt the ABS would be affected much and one could turn off ESP until the errant tire is fixed. One could also keep the spare very hard, say 45-50 psi, and if it had to be used, reduce pressure in the other 3 tires to say, 32 psi. Such action would probably reduce the difference somewhat, my guess is by 50% or more! Even doing this, you suould be able to drive normally at US Highway speeds (75-80) for hundreds of miles. I hasten to add that I'm not an automotive engineer so could be way off the mark here. 
Rob


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## PanEuropean (Nov 3, 2001)

*Re: Speedo Calibration---how do they do this! (Gobuster)*


_Quote, originally posted by *Gobuster* »_Lets say the outer wheel is turning a 62.5' diameter and the inner 57.5' (given a 5' track). The difference in rotational speed would be in the order of 6%, yet ABS and ESP don't seem to be confused by this maneuver.

Hi Rob:
A good point, but, the Phaeton knows when it is turning. It gets this information from two sources: First, from the steering wheel position sensor, which tells the stability system what direction you *want *to go in, and second, from the yaw rate sensors (electronic gyroscopes) that are located at the base of the B pillars, which tell the stability system what direction you are *actually *going in, and what your rate of yaw (heading change) is.
I think that cars that are equipped with ABS only probably have a fairly liberal allowance for wheel speed difference, because they don't have yaw rate sensors. But, cars with enhanced stability control systems, such as the Phaeton, probably have very tight tolerances for differences in wheel size due to the need for precise inputs to the stability control system. It is, however, possible that the car may compensate (self-calibrate) for differences in diameter of wheels when it is traveling in a straight line, and store any difference noted in memory.
Michael


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibration---how do they do this! (PanEuropean)*

What negative real-life effects would one observe if the system is getting screwy info such as an offset tire? . Would a message of some sort pop up on the screen? Or would the car computer get messed up badly?
Would other tires or the engine/transmission get placed under a strain that could cause horrible long term/short term damage?


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## Gobuster (May 19, 2005)

*Re: Speedo Calibration---how do they do this! (PanEuropean)*

Michael,
Good points! 
I wonder how manufacturers that offer ABS and stability control manage these systems when using a donut spare that is quite a bit smaller that the stock tire. For example, my Mazda RX8 had both systems (very effective I might add) and a spare at least 2" inches smaller in diameter to the stock wheel. Of course they recommended not going more than 50 mph on the spare, but thought that was due to the tire construction not the diameter difference. 
Rob


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## PanEuropean (Nov 3, 2001)

*Re: Speedo Calibration---how do they do this! (dcowan699)*


_Quote, originally posted by *dcowan699* »_What negative real-life effects would one observe if the system is getting screwy info such as an offset tire?

All I can guess - and this is strictly a guess - is that you would probably see a message on the Y24 display (the instrument cluster) to the effect of "ESP inoperative" or something like that.
I don't know if the driveline would suffer any physical damage, because I am not sure how the driveline is constructed. But, I have never seen a Phaeton or Bentley product with a 'space-saver' spare tire, and this leads me to guess that there are probably engineering (as opposed to computer related) reasons why the 4 tires need to be the same size.
Michael


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## Gobuster (May 19, 2005)

*Re: Speedo Calibration---how do they do this! (PanEuropean)*

An interesting subject and one I'd like to learn more about. 
As for drivelines, the very noun "differential" as it applies to cars, comes about from the different speeds the wheels turn when the vehicle is turning. If cars did not have differential gears, the wheels would drag when turning and tire wear/handling would suffer. Our Phaetons have differentials, between both pairs of wheels and, I think, between front and rear. This allows for various wheel speeds without tearing up the drive line. So, from a mechanical point of view, a smaller diameter wheel can be accomodated although it will "work" the gears more to compensate. I think the real issue is the ESP electronanny, it may try applying the brakes to the wheel turning faster thinking it's slipping - not good for pad life! Again, just guessing, I'll try to come up with some hard facts.
Rob


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## Paldi (Sep 4, 2004)

*Re: Speedo Calibration---how do they do this! (Gobuster)*

While you're at it, try to investigate why the Phaeton can't be towed with two wheels down! In other words, why won't the electronic differential locking devices disengage when it senses the car is being towed?


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## PanEuropean (Nov 3, 2001)

*Re: Speedo Calibration---how do they do this! (Paldi)*

I suspect that there are many reasons why the Phaeton cannot be towed on its own wheels - and lack of pressurized lubrication to the drive train is probably one of them.
Michael


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibraiton---how do they do this! (car_guy)*

Wow! My speedometer is 9.2% optimistic. I tested it twice. Once, I held the speedo on cruise at 70 mph, waited 30 seconds, then reset the data for the current trip data. It displayed that I was doing 65mph and never wavered from that. That is a 9.28% error.
Then I repeated that process while at 81mph on the speedo. It said on the trip data that I was doing 75mph. Again, around 9.5% error.
That means that I could have gotten to the Auburn Hills Phaeton GTG 1.33 hours sooner than I did and it would have been legal


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## car_guy (Aug 19, 2005)

*Re: Speedo Calibraiton---how do they do this! (dcowan699)*

I think you're doing the math wrong. 5mph error divided by 70mph indicated speed = 7.1% error. To check: 70mph indicated times .929 (this is 100% less 7.1% error) = 65mph.
This is the exact same error I see and I believe Michael sees.


_Modified by car_guy at 9:50 AM 10-4-2005_


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## chrisj428 (Feb 26, 2005)

*Re: Speedo Calibration---how do they do this! (dcowan699)*


_Quote, originally posted by *dcowan699* »_Would other tires or the engine/transmission get placed under a strain that could cause horrible long term/short term damage?


_Quote, originally posted by *PanEuropean* »_I don't know if the driveline would suffer any physical damage, because I am not sure how the driveline is constructed. But, I have never seen a Phaeton or Bentley product with a 'space-saver' spare tire, and this leads me to guess that there are probably engineering (as opposed to computer related) reasons why the 4 tires need to be the same size.


_Quote, originally posted by *Paldi* »_While you're at it, try to investigate why the Phaeton can't be towed with two wheels down! In other words, why won't the electronic differential locking devices disengage when it senses the car is being towed?

Let me start by addressing driveline differences and clarify some nomenclature.
VAG has two different quattro or 4Motion systems they use currently, one on longitudinally mounted engines and one on transversely mounted engines.
*TorSen Center Differential*
Audi A4/A6/A8
B5/5.5 Passat
Touareg (to an extent)
Phaeton
*Haldex Clutch Center Differential*
R32
TT
B6 Passat
A3
The TorSen differential has historically been the differential used by VAG. This distributes 50% of the power front & rear all the time. It has the ability to apportion up to 67% of the available power to either front or rear, depending on conditions. During steady-state driving, 25% of the power will be distributed to each of the four wheels.
This differential is mechanical in nature and has the ability to sense resistance as opposed to slippage and will apportion additional torque to the output with the higher resistance as opposed to away from the output with the lower resistance. (A concept I fundamentally understand but have a great deal of difficulty communicating to others). It is proactive in its responses.
The Haldex clutch is an electronically controlled center differential. Under steady-state driving (in VW's application), it will remain 100% front wheel drive (50% of the power to each of the front wheels) until intervention is required. 
Haldex has the ability to apportion 100% of the power front or rear, depending on what conditions dictate. It is reactive in its responses.
The electronic locking differentials referred to are used to manage side-to-side application of power on a given axle. This is essentially nothing more complicated that using ABS speed sensor information and pulsing the brake on the spinning wheel when a side-to-side rotational delta exceeds a certain limit.
You cannot use different sized tires on a vehicle equipped with a TorSen differential for the same reason you cannot tow the vehicle on two wheels (also the reason there's a sticker under the hood exempting the vehicle from two-wheel dyno emissions testing) -- the differential will constantly try to compensate for the speed differential and will be damaged (or in the dyno example, send all the power to the wheels not turning & launch the car -- ask anyone from the Front Range of Colorado what happened when the AIR Program first started







). 
I don't have access to the Haldex information, so I can't tell you directly what sort of damage would be incurred by forcing the differential to constantly comspensate for a front to rear speed axle difference for any length of time. I can tell you the Haldex requires a fluid change every 20,000 miles, something the TorSen doesn't.
There you have it...clear as mud.


_Modified by chrisj428 at 8:06 AM 10-5-2005_


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## dcowan699 (Nov 22, 2004)

*Re: Speedo Calibraiton---how do they do this! (car_guy)*


_Quote, originally posted by *car_guy* »_I think you're doing the math wrong. 5mph error divided by 70mph indicated speed = 7.1% error. To check: 70mph indicated times .929 (this is 100% less 7.1% error) = 65mph.
This is the exact same error I see and I believe Michael sees.

_Modified by car_guy at 9:50 AM 10-4-2005_

Ooops . You're right. I should've had my 10 year old do the mathematics. I was dividing the two speeds instead of the difference (5).


_Modified by dcowan699 at 11:26 AM 10-4-2005_


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## GripperDon (May 9, 2005)

*Re: Speedo Calibraiton---how do they do this! (Gobuster)*

PLEASE post pictures of the tires mounted AND tell us what you think of them. As you may have read before I really like them and have been considering them.
Thanks Don


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## PanEuropean (Nov 3, 2001)

*Re: Speedo Calibration---how do they do this! (chrisj428)*

Hi Chris:
Thanks for the *excellent *explanation of how things work. It is much appreciated.
Michael


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## GS340 (Oct 26, 2007)

*Re: (riccone)*

Has anyone ever figured out how to adjust the speedo? from reading the posts in this thread it appears that only the needle on the cluster is off. Mileage recorded, computer measured speed, etc.. is all correct.
My car is 7% high and I would like to adjust the cluster to display the correct speed.
thanks



_Modified by GS340 at 4:47 AM 7-3-2008_


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## Jim_CT (Jan 25, 2006)

*Re: (GS340)*

Save yourself some time - buy a Garmin Nuvi and throw it on the dash. Push the button to display the speed and you will see instantaneous actual speed in digital form. You also get Bluetooth speakerphone, and a newer nav system. Traffic reports, weather, gas prices, etc. are also available.
After using them for a while, you will correlate the Garmin speed with the Phaeton speedometer speed.
I have noticed the miles traveled as reported by the Garmin (Nuvi 680) are about 3% different than the miles traveled as reported by the Phaeton nav system.


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## PanEuropean (Nov 3, 2001)

*Re: (GS340)*


_Quote, originally posted by *GS340* »_My car is 7% high and I would like to adjust the cluster to display the correct speed.

Cannot be done. The 7% error is intentional, it is there to ensure that the speedometer never under-reads, even if the owner puts on larger-than-recommended diameter tires.
Michael


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## ciscokidinsf (Feb 17, 2008)

*Re: (PanEuropean)*


_Quote, originally posted by *PanEuropean* »_
Cannot be done. The 7% error is intentional, it is there to ensure that the speedometer never under-reads, even if the owner puts on larger-than-recommended diameter tires.
Michael

But I thought one of the VAG-COM comfort settings was there to let the Phaeton know if you had larger wheels for this purpose. no?


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## PanEuropean (Nov 3, 2001)

*Re: (ciscokidinsf)*

Yes, that is correct, but the error is there to protect VW against owners who do not have the appropriate re-coding done when they change wheel size.


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## GS340 (Oct 26, 2007)

*Re: (PanEuropean)*

Ok... so is there a way then to tell the computer that the car has smaller wheels? or xxx size?


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## PanEuropean (Nov 3, 2001)

*Re: (GS340)*

Yes, a coding change can be made to the instrument cluster to compensate for different total tire diameter. Normally, it is not necessary to change the default value if you are switching between 17, 18, and 19 inch wheels that are equipped with tires that conform to the specifications published for the Phaeton. This is because as the rims get bigger, the height of the tire gets smaller, thus the total tire diameter does not change by any significant amount.
If you fit unapproved tire sizes (e.g. 20 inch wheels), then total tire diameter changes, and a correction would be needed.
Michael


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## car_guy (Aug 19, 2005)

*Re: (PanEuropean)*


_Quote, originally posted by *PanEuropean* »_Yes, a coding change can be made to the instrument cluster to compensate for different total tire diameter. 

Michael,
Perhaps what Robert is getting at is that this might be a back-handed way to correct the 7% speedo error when using the standard tire size. Use the VAG-COM to tell the car 'x' diameter wheels (with 7% shorter circumference than the current wheel) are fitted and the error disappears.
If it is possible, I think it's a great idea. Is this something that can be discussed, or is it outside the range of what is appropriate for this forum? This potential fix could finally convince me to purchase a VAG-COM cable!
Steven


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## ciscokidinsf (Feb 17, 2008)

*Re: (car_guy)*

*CORRECTED. SEE BELOW FOR EXPLANATION*
To be accurate, it is NOT a variable value. You can either leave the value as is (17-18 tire) OR set the value to '8' = 19' tires. There is no adjustable value in the VAGCOM for the tires. _Right now, we are just assuming the 7% variance would go away if this value is adjusted_.
PS- Probably will not make a difference, it seems to be related to TPMS not speed. 


_Modified by ciscokidinsf at 4:06 PM 7-6-2008_


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## GS340 (Oct 26, 2007)

*Re: (car_guy)*

Correct. I would like to tell the phaeton the tires are xxx size or smaller then what the car is programmed for. 
Ciscokid, how would I explain to the dealer tech what menu to look under to make the change you are talking about. I've never used the software. 
I'm willing to try anything right now. Otherwise I might go with a 255/50/19 tire to correct the issue.



_Modified by GS340 at 12:32 PM 7-6-2008_


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## PanEuropean (Nov 3, 2001)

*Re: (ciscokidinsf)*


_Quote, originally posted by *ciscokidinsf* »_To be accurate, it is NOT a variable value. You can either leave the value at zero (17-18 tire) OR set the value to '1' = 19'-20' tires.

Hi Francisco:
What coding string are you referring to above?
Michael


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## ciscokidinsf (Feb 17, 2008)

*Re: (PanEuropean)*

It was discussed when we got the 'new tech tips' on TPMS and the controller. I had just gotten my 19" Bentley Wheels and we weren't sure what to do back then. (and I didn't change my values) below is the coding string and my question back to you:

_Quote, originally posted by *PanEuropean* »_
C00,Tire Pressure Monitoring System (J502) Coding "D"and higher suffix controllers 
C01,0?xxxxx - Region of Operation
C02,4 - North America (NAR)
C03,3 - Rest of World (ROW)
C04, 
C05,0x?xxxx - This value is always 1 (TPMS manufacturer)
C06, 
C07,0xx?xxx - This value is always 1 (end of assembly line)
C08, 
C09,0xxx?xx - Total number of tires to be monitored
C10,2 - 5 tires (vehicle has a full size spare)
C11,3 - 4 tires (vehicle has no spare tire)
C12, 
C13,0xxxx?x - Type of engine installed (this affects the minimum accepted tire pressure)
C14,0 - V8 NAR
C15,1 - V6 gas or diesel ROW
C16,2 - W12 NAR or V8 ROW
C17,5 - W12 ROW
*C18,8 - V10 ROW *OR* 19 inch tires with any engine - any country*
C19, 
C20,0xxxxx? - This value is always 1 (Full load specified pressures)
_ 
But I have a question:
OK, so now I have four 19" Wheels with the new sensors, and one 18" OEM wheel (the spare) with the old sensors. should I ALSO change the coding to:
- channel 18 value= 8 (what do I do with Channel 14? what's the value of C14 when you replace your tires to 19"? leave as-is?)_
I can't answer that question with any confidence.
My suggestion would be to go with what is known to work, which is the appropriate North American coding for your engine size. That is your best bet.
Michael


Maybe this would NOT make any difference in the speedometer. I just thought it was odd the TPMS coding had a value specific to 19" wheels in the TPMS controller values.


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## PanEuropean (Nov 3, 2001)

*Re: (ciscokidinsf)*

Ah, OK, now I understand what you are getting at.
First of all - I am the author of that label file. It has to do with TPMS performance only, nothing to do with the speedometer. I suspect that there is a different rate of temperature rise with the 19 inch wheels or the 18 inch wheels on the heavy V10, hence the difference in coding the TPMS.
Michael


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## unclepugh (Nov 7, 2008)

*How fast am I going???*

I have a 2006 V-8.
On a straight and level road, I engage the cruise control with an indicated speed of 60 mph.
Now I hit: tripdata....reset.....yes
The average speed number in the upper right hand corner of the tripdata screen should be the same as the indicated speed, right?
On mine, he tripdata average speed is always 3 mph slower than the indication on the speedo! It makes me wonder if the tripdata screen gets its info from the GPS rather than from the speedometer.

Which one is right, and why?????


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## PowerDubs (Jul 22, 2001)

German speedo always read high. The car knows exactly how fast you are going.. it just wants YOU to think you are a couple mph faster than reality so you won't speed.


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## Prince Ludwig (Mar 24, 2007)

The speed data that comes from the ABS sensors is pretty much spot on and is used my almost all of the car's systems. As Josh has pointed out, speedometers usually have a slight upward bias (I can't remember what the maximum figures is off the top of my head...)

Harry


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## PanEuropean (Nov 3, 2001)

unclepugh said:


> Which one is right, and why?


The answer can be found earlier in this thread, begin reading from page 1.

Michael


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## tomasty (May 24, 2011)

*Can the Instrument LCD display real-time speed?*

I wonder if Phaeton's Instrument LCD can display real-time speed? I thought it should, but below if the picture I got while I am driveing it. the zero just stays there and doesn't change. Any idea? the TPMS system on my Phaeton is not working, I wonder unless the LCD speed is using senser from TPMS sensor instead of feed data from the speed odometer?


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## fdtinc (Dec 31, 2010)

The TPMS sensors measure pressure inside the tire, so they couldn't be used for speed determination.
If the non-funtioning TPMS were the culprit, then through a lock-out of another function, not because of its own sensor defectiveness.
As to the speed display, hope someone chimes in, would be interesting to find out.

The TPMS is a joy: the fifth tire in the trunk has about 15PSI in it (on purpose to check), and the system displays all 5 tires OK. Know the other four are, and reset properly, but the spare shouldn't.....


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## rushcoil (Apr 17, 2011)

LOL... 

Just had to say that I completely ignore the TPMS now... sometimes it works, sometimes it doesn't, sometimes it shows two tires, sometimes 5... lol lol

One of my hobbies as of late is looking at Bentley GT's and Spurs on eBay and laughing at how every one of them has the TPMS light on, lol....


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## fdtinc (Dec 31, 2010)

rushcoil said:


> LOL...
> 
> Just had to say that I completely ignore the TPMS now... sometimes it works, sometimes it doesn't, sometimes it shows two tires, sometimes 5... lol lol
> 
> One of my hobbies as of late is looking at Bentley GT's and Spurs on eBay and laughing at how every one of them has the TPMS light on, lol....


LOL 2!
Will add that one to the list of time-waster to do....
As to the OK status on spare, when it should show a fault, will let the dealer "fix" it, still on warranty. that's what they're there for...


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## chillson (Sep 6, 2010)

Tomasty, while I do not believe there is a way to get real time speed displayed in the LCD, I do have a little trick to check your actual speed at any given moment. I usually do this when cruising at highway speeds. I have found that, at highway speeds, the difference between actual speed and what the speedometer indicates is about 5 mph. For example, if your speedometer says you are going 75 mph, you are really only going 70. You can check this by setting your cruise control (let's say to 75 mph on the speedo) and then resetting the short-term trip data. About 5 seconds after pressing the reset, the average speed will pop up and indicate your actual speed. Since you are travelling at a constant speed with your cruise control on, this is your actual real-time speed reading. You can reset the trip data as often as you like to check your speed at any given time. This whole technique assumes that the speed indicated on the trip data screen is more accurate than the speedometer...Jay


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## tomasty (May 24, 2011)

Chillson,

Nice trick, yes, I have noticed the speed difference between the speedometer and actual spped as well, but the way I found out is by using GPS data, I have used a Garmin GPS in my Golf and Mercedes, it can display real time travel spped, and I have noticed the speed on speeddometer is always 2-3km/h or even more faster than the GPS speed, this seems to be a comman way of German automaker to prevent you from getting a speeding ticket 

It is kind of disappointed to know that Phaeton can't display real time speed with it's LCD, my 2011 Golf can display realtime speed with it's black and white LCD, so as Mercedes, I am so used to looking at the speed from the LCD screen, I hardly check out the speedometer any more, Phaeton got a color LCD, it will be really handy if it can display real time speed. (Or even better like G force? haha)

Tomas


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## fdtinc (Dec 31, 2010)

No real need for a Garmin in a Phaeton?

Anyway, driving DC to NY over the weekend, used a Garmin in the Tiguan, which is bereft of goodies.

There, the Garmin consistently displayed 2mph MORE than was set on the cruise control.
Should not be, one's actual should not be greater than shown by the car.

To my knowledge it is illegal for the speedo to show LESS than actual speed, so unless something is not working right, it seems the Garmin is off.
If you go through speed - warning traps (the non-ticketed know how fast you're going kind), you can easily verify your speedo to actual, and I consistently find the speedo to overstate, as is common.

In Germany, I believe it is common for about a 5-10% faster display than actual, with a declining differentail at higher speeds.
Always thought this was a general car thing, not just in German cars or in Germany.


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## conmoto (Jul 8, 2009)

rushcoil said:


> LOL...
> 
> Just had to say that I completely ignore the TPMS now... sometimes it works, sometimes it doesn't, sometimes it shows two tires, sometimes 5... lol lol
> 
> One of my hobbies as of late is looking at Bentley GT's and Spurs on eBay and laughing at how every one of them has the TPMS light on, lol....


You really should spend the $349 for a VAG COM. Life is good now that I don't have to hear an annoying BEEEEP for the TPMS, faulty brake pad sensor, and the seatbelt (yes, I know I should always wear my seatbelt). It's so nice to hear nothing but the exhaust song from the 4.2 liters of engine. You can also easily lower your car to European spec. It's all a piece of cake with that little cable and a PC.


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## Cantrellc123 (Aug 5, 2012)

*Speedometer accuracy?*

I've recently acquired our 2nd Phaeton, an 06 V8. I've had my Garmin GPS in each of them. When in the W12 there is a 2 mph discrepancy from the GPS and a 4 mph discrepancy with the V8. Both cars show lower than the Garmin. To tell the truth I trust the Garmins accuracy more than the cars but I've no easy way to confirm which is correct. Both cars have OEM sized tires.
Can this be corrected if the cars are indeed at fault?


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## seawind3000 (Sep 17, 2010)

Hummmm The speedo's should read a shade higher then the GPS. They are required by law to read higher then the actual speed. If yours reads "low", then something has changed.

Mike


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## Cantrellc123 (Aug 5, 2012)

Mike,

Your correct, I was thinking wrong when I wrote that up. The cars are reading HIGHER than the actual speed indicated by the GPS. Why would there be a law like that?

Cantrell


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## seawind3000 (Sep 17, 2010)

Probability so you can't blame the speedo in court when you are trying to defend a 100mph speeding ticket  or something like that.

Mike


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## phaetonjohn (Oct 24, 2014)

With my metric speedometer, it constantly reads one tick over. So 80 km/h or under, it reads 3.333 km/h over. 80-200 km/h it reads 5 km/h over. And over 200, it reads 10 km/h over (Don't ask)
I determined this by setting the cruise control at different speeds, then resetting the SINCE START and seeing the average speed.

As long as you remember the "tick over" 'rule', you're good!!

-John


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