Hello,
I was looking at my spare tire today and noticed that it is at least 2 inches smaller than what I have now. I am running the stock wheels so I don't know why the spare would be so much smaller. It looks like someone took the wrong size tire and put it on that rim. OR do these rovers have 4 of the same rims and 1 of the stupid looking rims? Its a D I obviously 1995 3.9

 

Normally a D1 (in North America) will have 4 alloys, and 1 steel wheel. They are all the same size, 16x7. The steel wheel used for the spare is actually they same wheel that is used on base model discos outside of North America.

 

We need more info, you need to go and find out the actual tire size, write it down, for both the road wheels and the spare.
Stock size is 235/70R16, it will be on the side wall of each tire.

Also as tires wear they get smaller in overall diameter.