Original Tire size is 175/80R14 which no one makes anymore.
Acceptable tire size for 14" wheels are...
For 15" wheels,
For 16" wheel
225/50R16 Wow! This is really fat tire for 240D...
I suggest you use 195/65R15 for economy purpose... in tire and car's
aerodymanic impact of tires... the wider the tire you go.... the harder on
car... slightly less fuel mileage.
W123 chassis can accept all wheels from W126 cars... the S class of
1981-1991... with no problem... they are correct offset and fit perfect.
Which is why you have 15" wheels.