Distance Impulse Number

[ubercam]

Does anyone know how the Distance Impulse Numbers are calculated? For the record, I know my speedo reads high, but I'm not sure of the odometer's accuracy because believe it or not mile markers on the motorways in the UK are in kilometers! Luckily I can easily change my cluster in the MFD to km to do a quick test one of these days.

From experience and reading quite a lot about it, not to mention hours of searching on Google, I know the Mk4's have an external 43 tooth ABS tone ring and that on Mk5's it's somehow integrated into the wheel bearing or hub. I can't seem to find any reliable info online on how many pulses/rev it gives off. I've looked at pics of the wheel bearing and it's all smooth, no teeth to speak of except for the splines for the driveshaft (36 teeth if you were wondering).

I just can't figure out how VW comes up with their magic numbers so that I can figure out which number is best suited to my tire size (which btw is 15" European OEM 195/65/15). Just going from memory, I think it's currently coded to 3 (21960). From an online tire size calculator I know 195/65/15's are 634.5mm in diameter, 1993.3mm in circumference and do 502 revs/km.

There has to be some mathematical relationship between the tire's size and these magic numbers so I've tried various things in a spreadsheet and the nearest I can come up with that seems to make sense is actually multiplying the revs/km by 44. It seems to be arbitrary at this point unless that's how many pulses/rev and I've answered my own question without knowing it. If that's the case, my cluster coding should end in 2. Working backwards from the magic numbers, 3 = 21960, if you divide it by the revs/km 502 you end up with 43.75. I'll also concede that perhaps one of the magic numbers isn't a perfect exact match and it's just "close enough" which is fine, but I'd still like to know how much it's off by.

Just for reference, here are the coding digits and associated magic numbers, courtesy of Ross-Tech's wiki.

1 = 22188
2 = 22076
3 = 21960
4 = 21848
5 = 22304
6 = 22420
7 = 22532

Any ideas?

Thanks,
Cam

 

[D-Cell_Mekanick]

Read this: http://forums.tdiclub.com/showthread.php?t=316805. It has some useful information that pertains to your question. Plus there are numerous other threads about the same thing, do a search.

 

[ubercam]

This isn't one of your bog standard "ZOMG MY SPEEDO IS OUT BY X%!!1!" threads that we've all been seeing for the last 5-6 years. I spent at least 8-10 hours this weekend reading, searching and thinking about this (4 day weekend.. I got bored) and none of the posts you've linked answers my question. If I haven't found my answer by now, it's not on the internet in English, hence the reason I'm posting the question. I am looking for the mathematical relationship between the tire size (diameter, circumference, revs/km, etc) and the distance impulse number. I'm not worried about the speedo being off. I've got a GPS so I know how much it's off by. I just want my odometer to be as accurate as possible.

It took me a couple days to actually finish and post my question because I kept reading and thinking I'd find or figure out the answer but I haven't. For the record, this is my third VW in just about 10 years. I know the speedo is out from the factory and why it is that way. If my car had an Immo 3 cluster I'd have already bought a vagtacho cable and corrected the speedo error along with a few other things like taking the flat spot out of the temperature gauge, lit needles, etc. The day someone figures out how to mod Immo 4 clusters like that is the day I jump in and try it myself.

Either way I've emailed Ross-Tech to see if they, in their infinite wisdom, have any idea what the answer to my question is. If I hear back, I'll post their answer.

 

[Henrick]

The ABS sensor sends 48 impulses per wheel turn. All measurements in VW system is in kilometers, not miles. Sorry, don't know more info on this.

 

[Henrick]

To have everything in one place, it seems you have made some research earlier and shared your experience here: http://forums.tdiclub.com/showthread.php?p=3048698

 

[ubercam]

Wow I can't believe that I totally forgot about that!!! I suppose a lot has happened since last July... moved across the pond, got married, etc. I thought this all sounded like familiar territory, but I couldn't put my finger on it. It must also be the reason why I have a file called "Distance Impulse Multiplier.xls" on my USB stick which I discovered this morning.

I suppose I answered my own question about 10 months ago haha.

Thanks for dredging that up Henrick!

Cam

 

[Henrick]

Thank you for shining a bright light on such a dark feature/setting VW has invented!

 

[ubercam]

I've properly solved it! This is no longer a mystery!

I had a look in the VCDS label file for my cluster (1K0-920-xxx-17.lbl) and that gave me an insight into the higher numbered measuring blocks I didn't even know existed. I saw that measuring blocks 201 was for distance impulse number and 202 was for wheel circumference in mm. Sure enough, when I hooked up VCDS and read those blocks, they were exactly right!

Here's all the info I got from my cluster to save everyone the work.

* The DIN here is what the popup in VCDS says when you go into the text box to change the coding

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

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

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

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

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

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

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

I was surprised by a couple of things. Firstly, that I was actually within the thickness of my fingernail from being spot on with my assumptions and research prior to finding the measuring blocks. Secondly, the real DIN for 4 doesn't match up with what VCDS and every other bit of info online tells us. That's a number I've never seen before, but it's only for pretty big wheel/tire combos judging by the circumference of over 2m.

These numbers might vary from cluster to cluster and year to year, but others would have to post their findings for us to know for sure. If you want to help out, post your findings along with your cluster's part number, year, make & model. Please only post all the numbers if they differ, if they agree just the year, make, model and cluster part number is fine.

I don't have time tonight to match tire sizes to circumferences (especially since they use the mounted size, which makes online tire calculators inaccurate), but this at least solves the mystery behind these heretofore "magic" numbers. I've got an Excel calculator in the works and once it's ready I'll attach it to a future post.

Cam

 

[Henrick]

Uhm... Pretty confusing to me. So do you plan to investigate which number should be used for which tyre/wheel dimmensions in the future? If the mounted, inflated and pressurized tyres have different dimmensions, this is too tough to figure out for me

 

[ubercam]

Well, I'd love to have an exhaustive list of wheel/tire combinations vs. distance impulse numbers, but I'm at the mercy of other people doing their own leg work and sending me accurate data since I don't have 20+ different sets of tires to stick on the car and measure.

All I'm pretty sure of at this stage is that people running 195/65R15's and 205/55R16's (which are roughly the same diameter) should be using coding digit 3 for an accurate odometer. However, if they have access to VCDS they should still check measuring blocks 201 and 202 to see if the data matches what I found. If not, further investigation is required.

As far as I know, this data only applies to Mk5 Golf/Jetta/Rabbit models (1K platform). It may very well apply to other VW Group vehicles (i.e. Skoda, Audi, Seat) that share the 1K platform, but I can't be sure since I have no other vehicles to test. It might apply to other platforms as well like the Polo, Passat, Fox, etc, but again, without anything to test, I can't tell you for sure.

Cam

 

[Henrick]

All I'm pretty sure of at this stage is that people running 195/65R15's and 205/55R16's (which are roughly the same diameter) should be using coding digit 3 for an accurate odometer.

Thanks! This is mainly what I wanted to know!

 

[fussyoldf@rt]

Greetings Ubercam,
Thanks from me too for a sterling bit of research/deduction. My problem is that my odometer is over reporting by 5% the distance travelled which, of course, will shorten my warranty by the same 5%.
My tire research tells me that the true circumference of my 205-55-16 tires is between 1913 and 1936 mm which is the spread for various brands. let's say 1925 for an average. So the coding digit when/if I find it should come up as 6. To be as "wrong" as it appears to be the digit would have to be set at 4 which is the largest tire circumference they seem to be prepared for. Check my thinking for me here, if I want the thing to report realistically I want to change the number toward the code related to a smaller circumference. Alternately I need to change the tires to a larger circumference, like a 215-60-16 and that's quite a big change.
I have messages out to two people who have the VAG-COM equipment.

I've properly solved it! This is no longer a mystery!
I had a look in the VCDS label file for my cluster (1K0-920-xxx-17.lbl) and that gave me an insight into the higher numbered measuring blocks I didn't even know existed. I saw that measuring blocks 201 was for distance impulse number and 202 was for wheel circumference in mm. Sure enough, when I hooked up VCDS and read those blocks, they were exactly right!
Here's all the info I got from my cluster to save everyone the work.
* The DIN here is what the popup in VCDS says when you go into the text box to change the coding
Coding digit: 1
DIN*: 22188
MB 201: 22188
MB 202: 1938mm
Coding digit: 2
DIN*: 22076
MB 201: 22076
MB 202: 1948mm

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

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

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

Coding digit: 6
DIN*: 22420
MB 201: 22420
MB 202: 1918mm
Coding digit: 7
DIN*: 22532
MB 201: 22532
MB 202: 1908mm
I was surprised by a couple of things. Firstly, that I was actually within the thickness of my fingernail from being spot on with my assumptions and research prior to finding the measuring blocks. Secondly, the real DIN for 4 doesn't match up with what VCDS and every other bit of info online tells us. That's a number I've never seen before, but it's only for pretty big wheel/tire combos judging by the circumference of over 2m.
These numbers might vary from cluster to cluster and year to year, but others would have to post their findings for us to know for sure. If you want to help out, post your findings along with your cluster's part number, year, make & model. Please only post all the numbers if they differ, if they agree just the year, make, model and cluster part number is fine.
I don't have time tonight to match tire sizes to circumferences (especially since they use the mounted size, which makes online tire calculators inaccurate), but this at least solves the mystery behind these heretofore "magic" numbers. I've got an Excel calculator in the works and once it's ready I'll attach it to a future post.
Cam

 

[Fueldog]

Thanks Ubercam, curious as I'm in the middle of wanting to change my distance impluse settings. when looking at one of your earlier posts about a particular tire size you stated. I was comparing your 195/65/15 showing 503 rev's per km. However when I looked up that tire it shows to have 517 rev's per km. Was that a typeO or did I miss something. I currently have installed 205/60/16 with 2051mm circum 503 rev/km on 2011 Jetta TDi and now I have a 5km speed error, showing slower than actual. Wanting to change impluse settings however I'm new with the VCDS and not sure where to reach the number changes etc. Still studying, appreciate all you have shared. Might you share or have more to be of help for me? Thank You Ric

 

[Henrick]

I have sent Ubercam a private message a few months ago but did not get any replies. Seems he is no longer a visitor of the forums (so sad).

If you reread all his posts, you will find that mounted tyre revs per kmm is different from what all online calculators specify because that is for unmounted, uninflated and unloaded tyre.

FYI, your new Jetta uses a little bit different coding. It is no longer numbers from 1 to 7 but instead VCDS lists all those options as for different cars. If you are able to verify the error your tyres/car produces, my suggestion would be just experiment with different values and find the closest one. Note, that you need to check the odometer reading, not the speedo! Speedo will be off in any case, this is a programmed error.

 

[ubercam]

Wow a blast from the past!

Sorry for not answering the messages guys, I must have disabled the email notifications or lost them in the shuffle.

I remember doing all that research in my moms car like 5 or 6 years ago. I probably still have the spreadsheet someplace. I recall looking through VCDS measuring blocks for ages and found the clues somewhere in the 200s. I think the system uses the ABS ring to count impulses and multiplies the numbers by the value you choose in VCDS. I remember the MK4 had a ring with 43 segments, dunno about newer models.

I remember testing each setting against the odometer check east of Winnipeg along the Trans Canada which was near our house at the time.

Henrick is correct that it's not the speedo you want to adjust its the odometer. The speedo will always be wrong due to EU law. All European cars have this problem. The only way to get it accurate is to either download the firmware for the instrument cluster and modify the curve (difficult/impossible on newer models, MK4 less so), use a GPS, or install something like the Fiscon Bluetooth Hands free kit which includes the E-MFA add-on which shows your true speed, boost, fuel remaining in L or gal, engine and oil temps etc. You need the cluster with the full height screen though. There may be others as well but I'm not aware of them.

If you're OK with the mental arithmetic just dock about 10% from the speedo reading once you get the correct setting and that's close enough to your actual speed.

Hope that helps.

 

[bl00tdi]

I adjusted my distance impulse number by changing it until the OBD-II speed matched the GPS speed as closely as possible. The Torque app for Android makes it super easy to compare the two at a glance and it was off with the default setting after I upgraded to 17" wheels. Simple, and no math or spreadsheets required. I agree though that this setting has nothing to do with the mechanical speedo but mileage calculation.

 

[ubercam]

Hi guys

I made a Google Sheet which explains everything.

I'm not sure exactly how to share a read-only spreadsheet with certain cells unlocked for you to change but which don't save. Either way I've granted View rights to it. It may mean you have to make a copy to your own account to use it. If you find it too annoying I'll turn it into an Excel spreadsheet and attach it.

Enjoy
Cam

 

[ubercam]

As I've had a private request for an Excel spreadsheet, here it is!

 

[VladaR983]

Is this open topic?? Pls... i cant download your Excel and i am a bit confused too... can you help me ... i have Golf 5 and tire's are 225/45 R17... what code should i use? My speedo lie very much.... when speedo show for example 150 km/h my gps show maybe 130

 

[turbodieseldyke]

The google sheet link in post #17 works.

 

[drewpul]

does anyone have that spreadsheet? The link is now dead.