First, the tyre size. Two different sizes of tyre were originally fitted to this model of car. The size of tyre is either 235/55R18 or 225/60R17. This is because there have been two different sizes of wheel hub fitted. One type has a diameter of the metal hub of 18 inches, the other 17 inches.
You can check the size of the fitted tyres by looking for a set of letters and numbers, with the slash in the middle, in big writing on the side of your tyres.
The bit above, is the metal dish that holds the bottom of the spring? Try passing something between it- such as a bit of cardboard. If it's not touching (and it won't be, because, as you say, you'd have worn down that bit of tyre) then everything is ok.
Incidentally, if you look at blackcircles.com (who sell tyres online), and put in your car registration, it should tell you the size of tyres that your car needs.
The reason you can see so much spring is that the body is higher than a saloon car. This means the wheels have the space to travel up and down if you're driving off road.
The only issue that I can see is that if the tyres are 5 years old then they may start to perish very soon - but they will have been checked when you had your last MOT.
: o )