i found a tyre shops near my place that have 3 brands of 195/50/15 and 1 195/45/15 so im off measuring tomorrow to see if any are under their advertised sizes (fingers crossed) will let everyone know the outome.
as i still want the widest rubber as it has traction trouble as it is.

As explained by the other guys
They will 10mm or so smaller diameter. Same width generally.
The 45 is percentage of tyre width. So 45 = 45%

Some websites show the dimensions:
Bridgestone Website RE555

I understand "technically" that tyres of supposedly the same size ie: 195/50/15 or whatever are meant to be the same size, but over the years my experiences have show that there is a distinct possibility that they may differ in size a little. (large 4x4 tyres i have found can be upto 2" different)as im only after a few mil i might find what im after:)