The lifespan of semi-trailer tires varies based on several factors, including usage, load weight, road conditions, and maintenance practices. On average, semi-trailer tires can last between 3 to 7 years or approximately 100,000 to 150,000 miles. Regular maintenance, such as proper inflation, regular inspections, and timely rotations, can extend the lifespan of your tires. It's essential to replace tires that show signs of significant wear, damage, or aging to ensure safety and optimal performance. Always consult with a professional to assess the condition of your tires and determine the best replacement schedule.