No, you should never put trailer tires on your passenger car. It is a dangerous practice that compromises safety. Trailer tires, designated with an ST (Special Trailer) prefix on the sidewall, are engineered for fundamentally different purposes than passenger car tires (marked with a P). Using them on your car creates significant risks due to mismatches in load capacity, speed rating, construction, and tread design.
The primary danger lies in the load capacity and speed rating. Trailer tires are built to handle heavy, constant loads at relatively low, sustained speeds. Passenger car tires, however, are designed for dynamic forces: acceleration, braking, and high-speed cornering. An ST tire's sidewall is too stiff to provide the necessary grip and comfort for a car, and its speed rating is typically too low (e.g., 65 mph or 75 mph), making a blowout at highway speeds a real possibility.
Furthermore, the tread patterns are incompatible. Trailer tires often have a simple, ribbed pattern optimized for rolling straight and supporting weight. Car tires have complex tread blocks and sipes to channel water, provide cornering grip, and ensure safe braking distances on pavement. Using a trailer tire would result in dangerously poor wet-weather handling and significantly longer stopping distances.
| Feature | Trailer Tire (ST) | Passenger Car Tire (P) | Risk of Mismatch |
|---|
| Intended Use | Carry heavy, steady loads on an axle | Handle dynamic forces (steering, braking) | Loss of control, poor handling |
| Speed Rating | Typically L (75 mph) or M (81 mph) | Typically S (112 mph) or T (118 mph) | Overheating and blowout at high speed |
| Sidewall Flex | Very stiff to prevent sway | Softer for grip and comfort | Harsh ride, reduced traction |
| Tread Pattern | Simple ribs for straight-line stability | Complex patterns for wet grip and cornering | Poor braking, hydroplaning risk |
| Load Capacity | High, for weight burden | Balanced for vehicle weight and performance | Incorrect load distribution |
If you need a temporary spare, always use a tire approved for your specific vehicle, such as a compact temporary "donut" spare or a full-size matching tire. The correct tire is critical for your safety and the safety of others on the road.
