yep ..... and being honest they arn't imperial sized either , i should bloody know that .
a road tyre size the isn't the actual size and the side wall is a percentage of the width , where as the slick sizes are actual sizes in mm , so ignore my calculator its crap ...
the middle dimention on a slick is an sctaul measurement .....
thats why there is no real conversion ...
take 4 different 195x50x15 road tyres and i be they all have different widths and profile heights
as for how they are treated , if they are still decent we would use them for testing , if they were shot they would be sold or binned
it depends on what they are off and what sort of budgets are being spent .... but the variation in second hand slicks is unreal , and the truth is they are all worth nothing but people get beer money for them, most times someone has been given them by a team and is then selling them on .