CD 3 wheels, which tires?

hello, my name is alfred hamstra
new on this forum
I drive a VX spider
im from the netherlands, sorry for writing in english...
I can speak german, but writing is a bit of a pain...

my question is for another spider. I have a set of original CD3 wheels
Im looking for the right tires on them...
Am I calculating correct?
My VX has a perfect reading of the KM dial on 205-50-15 wheels
So it has a total of 24 cm middle to end of the tire (half of 15" is 19cm plus 5 cm)

So i guess in order of having another perfect reading of the dial, my CD3 wheels should have tires of 185-75-13

BUT, i have a set of steel wheels laying, which have tires on them of 165-80-13, some even with 82...

Any one any thoughts?

regards

alfred