Potenza

If you have an original wheel the offset should be stamped on the back of the wheel (either the barrel or spoke). It will probably just be a number and a letter like 30P or 40P.

Exactly Rolls

Teach you? Your already well on the way. That is the stupidest thing I have ever seen.

Not true. You will lose grip all round. Tyres are designed by computers - The whole design process is based around a certain range of rim width sizes. If you put a tyre on a rim that is to large you will make the tread surface convex, on a rim that is too small you will make it convex - effectively removing tread therefore grip from the road surface. That is why the shape of sidewalls has evolved - to create an omptimum contact patch with even contact pressure on the recommended rim widths.

when you put a tyre on a rim that is larger than recommended you will distort the tyres contact patch - reduce grip/stability and encourage irregular wear and run the high risk of popping the tyre of the rim.

225/50R16 approved rim contours are 6J" through to 8J" with 7J being the nominal.