Buy 3 Tires, Get 4th Tire Free Instantly Buy 3 Tires, Get 4th Tire Free Instantly. Receive a discount equal to the price of a single tire when four tires are added to the cart. Valid on select in stock tires only. Those tires for which discount is available will be identified in search results & product detail pages. All other tires and special order tires are excluded from this offer. Valid when scheduled for installation on PepBoys.com and installation is completed between 5/1/17 through 5/28/17.