Per the thread:
09 onwards? You have to cut the brown/black striped wire on the speedo connector and leave it cut to enable access to the wheel size function.
To adjust the wheel size
1- press MODE to go to TRIP 1
2- Hold the MODE key for around 10 sec
3- It will show actual wheel size. Use the MODE key to increase the wheel size and the SET key to decrease it
4- Hold the MODE and SET key to exit
The default size on the 990R is 2205mm circumference for the 21" wheel.
19" - 2040 mm
17" - 1882 mm
so if yours is 10% out, adjust the circumference figure by 10% and go try again :)