Tread depth is the primary indicator of a tire's health. New tires typically start with of tread.
Tires degrade over time due to environmental exposure, regardless of how much tread is left. How to Buy Tires: A Step-by-Step Guide - US News Cars when to buy new tires
Many experts, including Tire Rack and SimpleTire , recommend replacing tires at 4/32" , especially if you drive in wet or snowy conditions where traction drops significantly below this point. Quick DIY Tests Tread depth is the primary indicator of a tire's health