Speedometer adjustment/calibration?

[mrx]

Does anyone know how to adjust/calibrate X1's speedometer to get correct readings after changing 2" bigger rims & tyres?

[fiehlsport]

Can't be done.

[vstolpner]

Use an old phone and a GPS based speedometer app. That's about it

[bucketfoot]

Did the diameter actually change?

Normally when you increase the size of the rims you decrease the aspect ratio, which more or less keeps the diameter unchanged.

[d1saster]

Yes it can be done via coding.

[rps]

I put non run flats and sport wheels on my Z4 that were larger than the OEM wheels and tires which resulted in a correct speedo reading verified with my GPS instead of the speedo reading 2-4 miles higher than my actual speed.

[0w40X1]

Originally Posted by mrx

Does anyone know how to adjust/calibrate X1's speedometer to get correct readings after changing 2" bigger rims & tyres?

The speedo is approx 5% high already, so bigger tires will make the speedo MORE ACCURATE OR SLOW IT DOWN.
.

You can put a scan guage on OBI plug, and calibrate that.

You can check speedo by getting car to hit mile markers in one minute, then, reading speed (use calculator to get percentage difference).

Odometer is accurate stock, so whatever bigger tires percentage will SLOW MILES SHOWN.

[fiehlsport]

Originally Posted by d1saster

Yes it can be done via coding.

Source? Have not seen any solution to this whatsoever and it is a highly debated topic due to BMW speedometers being off by a few mph.

If this was true it would be a very popular coding mod.

[d1saster]

KOMBI KMBI_PL2.C09
C08_K_ZAHL_TACHO - IMPULSES PER KILOMETER FOR SPEEDOMETER
Default is wert_06
Changed to wert_01

C08_K_ZAHL_TACHO_KOMPL - IMPULSES PER KILOMETER FOR SPEEDOMETER (COMPLEMENTARY)
Default is wert_06
Changed to wert_01

The result is speedometer difference of 1 mph at 80 mph. Pretty close to me. The reason many E90 people claim it can't be achieved is because they have to flash KOMBI module to latest version in order to have more than two values under the above listed options. Some tried to add custom values but KOMBI doesn't like custom numbers and returns error in BC.