VCDS Rolling Diameter adjustment

[kaanage]

Given the lack of response in the Wheels/Suspension forum, I thought it wouldn't hurt to repost my query here.

I'm looking at getting 14" rims so that I can go down to a 165/70R14 from the OE 195/55R15 on my 9N3 Polo.

This will make my speedo and, more importantly, odometer under read by about 1.5% so I'm hoping someone can help me with the VCDS adjustment to correct this

If I could get 165/75R14 tyres, then I'd leave it as this would gear my car up by 1.3% but nobody makes them (not for passenger cars, anyway). I'd rather not have to go up to 175/70R14 (raises gearing by just under 1%)

[bazzle]

Most VW speedos seems to read under. Do a gps check 1st and you may be better off with the bigger ones.

[Select]
[17 - Instruments]
[Recode - 07]
Write down the existing coding for future reference.
Drop down box shows what digit to change.

Then go for a drive with gps to confirm.

1 = 4345 impulses/km
2 = 3528 impulses/km
3 = 4134 impulses/km
4 = 3648 impulses/km
etc

Bazzle

[kaanage]

Thanks Bazzle.

I am more concerned about my odometer. I KNOW that the speedometer underreads and I can easily allow for this but I want my odometer to be consistent with my OE tyres.

Do you know if that recode affects the odometer or just scales the speedometer readings?

[wai]

On my new Caddy, the digital speed read out is a consistent 5 km/h over the actual speed when measured against my AlerteGPS unit.

I have tested the AlerteGPS at the speed gantry just south of Albury on my many trips between Sydney and Bendigo, and it matches the gantry speed very closely (within 1 km/h).

I am in two minds about getting the dealer to adjust it as it is a consistent 5 km/h over right from 40 km/h through to 110 km/h. As a result I have set the AlerteGPS to just give me the audible warnings of things like speed cameras, school zones and the like. The 5 km/h gives me a good tolerance.

[Corey_R]

Please note that kaanage titled this thread "rolling diameter adjustment" and not "speedo" adjustment. This is because he already knows you cannot fix the built in speed error via VCDS. Attempting to do so will cause your ODO and all trip meter functions, including fuel figures to be incorrect. Those topics have been discussed numerous times around the forums if you'd like verification of my statement.

The function does work for correcting rolling diameter changes though.
Cheers.

[kaanage]

Thanks Corey for both the clarification and the confirmation - both are much appreciated

[bazzle]

Thanks Bazzle.

I am more concerned about my odometer. I KNOW that the speedometer underreads and I can easily allow for this but I want my odometer to be consistent with my OE tyres.

Do you know if that recode affects the odometer or just scales the speedometer readings?

From memory on VWs earlier Bulletin for tyre size adj using this function it stated odo not affected.

Bazzle