Tires should be replaced when the tires remaining tread depth is approximately 5/32 seconds in the snow, 4/32 seconds on the wet roads, and 2/32 seconds on dry roads. Tires that have a bubble, bulge, crack or dry rot must be replaced. Any uneven tread wear, or inner and outer side wall damage means it's near the time to replace your tires.
Measure your tire tread depth with a depth gauge. If you don't have one, try the "penny test." Insert a penny into the tire tread grooves with Lincoln's head facing down. If you can see the top of Lincoln's head, it's time to replace your tires. You can do the same test with a quarter, using Washington's head. If you see Washington's head is partly covered by the tread, you'll know you have at least 4/32 seconds of an inch of tread remaining.
Call for current tire specials. If you buy 4 tires, the mount and balance is free!