Tires: new tire positioning, dry pavement, wet pavement

Question
I have heard on a couple of occasions recently that if purchasing 2 new tires for front wheel drive auto, those tires should be mounted on the back. What is the story, please?

Answer
It has to do with differences in traction levels in adverse conditions.

On dry pavement, the traction differences between new tires and worn tires is relatively small, with the advantage with the more worn tires.  But that hardly ever is an issue,

But on wet pavement - where hydroplaning becomes an issue - or in snow, you never want to lose traction in the rear - you just can't recover if your rear end comes around on you.  So you want the best tires for traction on the rear.

Hope this helps.