Vectra B - instrument cluster

[neno]

I have an old Vectra B, 1997, 1.6 8V, on which I installed a 1.6, 16V instrument cluster because this old one did not have a tachometer. Now it shows 6km/h higher speed because the car it was taken from has bigger 165/70/15 wheels and my car has 175/70/14. Which "opcom" has the ability to adjust the circumference of the wheel, because I can't find that option with what I have?

[timoton]

you need to write eeprom via opcom with proper data
or read/save eeprom, change some hex values and write back
unfortunately, i don't remember, which bytes to change
or try to find dumps for your cluster on the internet

also, you can find table with model variants here opel-infos.de