There isn't a fixed schedule, as tire lifespan depends on factors like your driving habits, climate, road conditions, and the tire's design. However, most manufacturers recommend inspecting tires annually after five years of use and replacing them at a maximum of 10 years, even if they appear to have tread left, as rubber degrades over time.

Key indicators include tread depth falling below 2/32 of an inch (you can use a penny – if you see all of Lincoln's head, it's time), visible tread wear indicator bars becoming flush with the tread, cracks or cuts in the sidewalls, bulges or blisters appearing on the tire surface, and experiencing unusual vibrations while driving.

Driving on worn-out tires significantly compromises your safety. The risks include drastically reduced traction, especially in wet or snowy conditions leading to skidding; increased braking distances; a higher likelihood of hydroplaning; and a greater chance of tire punctures or sudden blowouts, which can cause a loss of vehicle control.

It's generally recommended to replace all four tires simultaneously for optimal handling, stability, and even wear, particularly on all-wheel-drive (AWD) vehicles where mismatched tires can damage the drivetrain. If replacing only two, they should be the same model as the others and installed on the rear axle for better vehicle control.

A professional tire replacement service usually involves removing the old tires from the wheels, mounting the new tires onto the wheels, and then balancing each tire and wheel assembly to ensure smooth rotation and prevent vibration. It often includes new valve stems (for most standard applications) and proper inflation according to your vehicle's specifications, along with the responsible disposal of your old tires.