Kroggers:
I have found that the tire size designated by each manufacturer is rather arbitrary, and there is a huge tolerance allowed. Very much like oil viscosity ratings (not to start an oil thread!).
Anyway, I use tirerack.com
Tires by Brand at Tire Rack
to check actual section width and some tread width data. Unfortunately it is all in American dimensions.
In checking the 265/18 sizes, a R888 is a 10.8" section width vs. an MPSC at 10.9", so the MPSC is a bit wider, but not by much. This is pretty close by tire size standards. Perhaps your wheel offset was a bit different also.
Anyway, I have been to Finland before, and work in the paper and biomass fuel energy field so I have many friends and acquaintances who are Fins, and know some Swedes and Danes too. One Fin that I work with here used to race Porsches in Finland, and he ships some used cars and parts to Finland on a regular basis. I will send you a PM.