Useful videos re: replacing 2/4 all season tires or winter tires
 

Just posted one of these in another post here, thought they deserved their own post, can't believe I haven't done so before. I'm a tire wholesaler, and hear frequently from customers about the fights they have regarding replacing 2 or 4 tires with their retail customers. I frequently direct them to these videos.

I've been on this test track in the video at Michelin's proving grounds in South Carolina and done this exact test. The control their driver with the worn tires in the rear shows in some of the video(1:07) is really good, there really is NO warning when this happens to a normal driver.

YouTube - hydroplaning

Good Tire Rack winter tire demo:

YouTube - Tire Rack Tire Test - Winter Tires: Mixed vs. Matched Tires