As far as I know, the correct offset for Suds is +39mm.
This is where the mounting face of the wheel on the wheel hub is 39mm further to the outside of the car than the centreline of the wheel.
Wheel offset is generally known now as ET due to the adoption of the German offset index.
ET is an abbreviation of the word Einpresstiefe or somesuch which means something like "press or stamping depth"
The lower the + figure, the larger the Carlos Fandango Factor (you probably have to be old and British to understand this index).
Low offset numbers mean that the wheel pokes out of the arches more for a given wheel width and on a FWD car is more likely to rub on the wings.
Old rear wheel drive cars have low offsets (escorts +20mm) and wheels tend to have wide lips around the rims (four spoke RS wheels, Revolutions etc)
High offset numbers mean that the wheel is sunk into the arches more for a given wheel width and on a RWD car is more likely to rub on suspension members.
New and front wheel drive / four wheel drive cars have high offsets (Vauxhalls +49mm, Subaru +53mm) and wheels tend to have spokes flush with the rims (e.g most cars these days)
I have 15" 4 x 98mm wheels from an Alfa 164 Twin Spark on my Sud (1 standard set ET+40, one 5 spoke Zender set ET+30) that fit no probs and a set off a Maserati Biturbo (6 x 14", 4x98mm ET+6mm) that look the dogs but probably won't fit.