found on Tire Rack
"When tires are replaced in pairs in situations like these, the new tires should always be installed on the rear axle and the partially worn tires moved to the front. New tires on the rear axle help the driver more easily maintain control on wet roads since deeper treaded tires are better at resisting hydroplaning."
Thats just a ploy to sell more tires. In water the front tires are gonna clear a path for the rear ones somewhat so the rear won't have as much water to deal with. If you always try to keep the best tires on the rear you will never be able to rotate them either as most vehicles wear out the front faster, especially front wheel drive cars. I have seen people with FWD never rotate their tires and most of em will replace the rear ones 1 time for 4 front pairs.
