Ive no spare wheel on my car transporter trailer and tonight the inevitable happened and I punctured, fortunately I was close to home so it was ok but its got me thinking. The wheels are 13s with 175/80s with 114.3 pcd.
A quick look on the web shows no one selling this size wheel. However I have 5 nissan alloys of this PCD, albeit 15" with 195/60 which is very close in size. Can I use these on the trailer ( or am I dreaming)

As long as the offset allows you to fit the wheel & tyre under the wheelarch you might be in with a chance.

There is a useful tyre size calculator here to see if the diameters are close.

13/175/80=21.3"
15/195/60=24.2

Hmmm quite a difference

Actually its more wether the car tyres are up to it than the rolling diameter that my concern

I doubt that would be a problem as long as you don't overload the trailer.

I think you have 5.5inch PCD wheels.
http://www.towsure.com/product.asp?p=7087