When you look at the sidewall of a trailer tire, you’ll see a string of characters like ST225/75R15 LRE. It looks like code, but it’s actually a roadmap for your safety. Here is exactly what those numbers mean.
1. The Prefix: ST
Most trailer tires begin with ST, which stands for Special Trailer.
- Why it matters: ST tires have stiffer sidewalls than car tires to handle heavy loads and prevent the trailer from swaying.
- Note: Never swap these for “P” (Passenger) tires.
2. The Size Sequence: 225/75R15
This is the “physical footprint” of your tire:
- 225 (Width): The width of the tire in millimeters.
- 75 (Aspect Ratio): The height of the sidewall. Here, the height is 75% of the width.
- R (Construction): Stands for Radial. If you see a D, it means Bias Ply.
- 15 (Rim Size): The diameter of the wheel in inches.
3. Load Range (The Weight Capacity)
You will see a letter like LRC, LRD, or LRE. This tells you how much weight the tire can safely hold.
- Load Range C: 6-ply rated
- Load Range D: 8-ply rated
- Load Range E: 10-ply rated
- Rule of Thumb: You can always upgrade to a higher letter (more capacity), but never go lower than what your trailer manufacturer recommends.
4. The Speed Rating
Often overlooked, a single letter tells you how fast you can safely drive.
- J: 62 mph
- L: 75 mph
- M: 81 mph
- Tip: If there is no letter, assume the speed limit for that tire is 65 mph.
5. The DOT Date Code (The Expiry Date)
Tires rot from the inside out. Find a 4-digit number at the end of the “DOT” string (e.g., 1426).
- 14: The week of the year (14th week).
- 26: The year (2026).
- Safety Check: Replace trailer tires every 5 to 6 years, even if the tread still looks “new.”
Quick Specs Table
| Code Segment | Example | Meaning |
| Prefix | ST | Special Trailer |
| Width | 225 | 225mm wide |
| Aspect Ratio | 75 | Sidewall is 75% of width |
| Construction | R | Radial |
| Wheel Diameter | 15 | 15-inch rim |
| Load Range | E | 10-ply equivalent |
Pro Maintenance Tip
Always check your tire pressure when the tires are cold (before driving). Most trailer tires perform best and stay coolest when inflated to the Max PSI listed on the sidewall.