Wheel offset

[tc49]

Hi All
Want to get a new set of alloys....bigger ones...but am a bit confused about the offset.
I am going bigger on alloys and lower on the profile of the tyres so that the speedo is not compromised. I have the 9n standard alloys but want to go either 15inch or 16inch. What should the offset be for those size rims. I will be keeping it standard, not lowering it!! Come to think of it....what in the standard offset of the wheels. Looked in Haynes but could'nt find anything.
Appreciate your advice
Terry.

[tc49]

Did I put that in the wrong forum???? Sorry
TC

[david burton]

probably about 40 offset