# Tire Size coding



## Krzysiek_KTA (Mar 20, 2014)

Good Day All,

I have replaced the stock 225/50R17 tires with 225/45/R17.
Is there any way to code new tire sizes into the car, so the distance/speed/range/consumption reading will be more accurate?

Many Thanks.
Kris


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## gIzzE (Aug 10, 2003)

Probably easier to just adjust it in the cluster to take account for the new rolling radius. 


Calibrate BMW MPG 


1. Hold down the odometer reset button and turn the ignition on by pushing start/stop button.
2. Release the odometer reset button, and you should see a menu of 4 items on the dashboard. From here on, use the odo-reset button to advance to the next entry through a short press, and to select through a long press.
3. Choose the one that says Unlock through the above, which will take you to a passkey screen. Your passkey is the sum of the last 5 digits of your VIN. Increment the two-digit number until you get to it, and with the long press of the odo button, select it.
4.then scroll down to correction factor and modify it from 1000 to whatever you require, mine is at 964 and it's now almost spot on every fill up.

Standard factor is 1000 going up above 1000 reduces the mpg on the dash, below 1000 increases the mpg reading. 

I got this from someone else but it worked for me. The OBC on mine was 5 - 7% optimistic, so I changed it from the default setting of 1000 up to 1060 (so -6%) and now the OBC is rarely more than 1% away from the brim to brim measurement.


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## dmnc02 (Mar 28, 2003)

Or try ICM > C_Dyn_Rollradius


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## Krzysiek_KTA (Mar 20, 2014)

Many Thanks,

I'll try both ways and see.

cheers

Kris


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## Krzysiek_KTA (Mar 20, 2014)

I coded ICM 300 C_Dyn_Rollradius

I have changed the parameter from 32cm to 31 cm and the entire car measurement are correct.

For sanity check I have also physically measured the diameter of the wheel with new tire set
(225/45R17) and it was exactly 62cm

I run through several speed camera measurements and the cluster speed was never more than 1 mph different ( lower) than the measured speed. I have also checked the the cluster speed against GPS and also the error was within +_ 1mph.

Many thanks for your leads.

cheers

Kris


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## d1saster (May 17, 2016)

On a 2016 X6 I coded ICM 300 C_Dyn_Rollradius from 36 cm to 34 cm without any effect. I also tried with 31 cm and also no effect. The car has a digital cluster (DKOMBI) so no analog speedometer is present at all. I changed BC_V_KORREKTUR to nicht_aktiv and the error got reduced from about 5% to 3.5% but still significant. I couldn't find correction factor that govern the digital needle.

I know it is a different car but I am hoping somebody have some knowledge about that.

Thanks


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