Perhaps this is a naive question, but my entire life I've never dared buy anything but stock-size tires...

My VDP has 225/60R16 - what would happen if I swapped them with lower profile 225/55R16 or 225/50R16? How about a wider 245/50R16, can that go on the stock 16" VDP rims? What would the effects of that be?

What would happen if I only do 2 and leave the original size on the front?

 

225/55R16 will probably not much of a difference, just a slightly lower side wall / slightly large gap in the wheel well.
Jaguar offered a 225/55R16 as a "sport" tire over the 225/60R16 on the final generation XJ-S, guess that says some.

225/50R16 will look rather strange, your wheel well will be rather empty.

Although they will fit, 245 is too wide for your 7J rims, 225 is really the practical max of those rims.

Time for larger rims ...

 

"What would happen if I only do 2 and leave the original size on the front"

Plenty of possibilities, none of them good.

 

lol, Mark please describe the issues

So if I need to do budget for all 4, and can't go wider, what is the benefit of just lower-profile? 225/60 -> 225/55?