ST Trailer Tire Sizes Explained: What the Numbers on Your Trailer Tire Mean
An ST tire size like ST205/75R15 reads: ST = Special Trailer (trailer use only), 205 = section width in millimeters, 75 = sidewall height as a percentage of width, R = radial construction, 15 = wheel diameter in inches. The correct size and load range for your trailer are listed on the trailer's VIN/certification plate.
The anatomy of an ST tire size
Take ST205/75R15 — the most common trailer tire size in North America:
| Part | Meaning |
|---|---|
| ST | Special Trailer — engineered for trailer axles only, never for drive or steer positions |
| 205 | Section width in millimeters (~8.1") |
| 75 | Aspect ratio — sidewall height is 75% of the width |
| R | Radial construction (bias-ply versions use a D, e.g. ST205/75D15) |
| 15 | Fits a 15-inch wheel |
After the size you'll see a load range letter (C, D, E…) or a ply rating (6PR, 8PR…) — that's the strength spec, covered in our load range guide.
The sizes that move in Texas
From our Dallas warehouse, five sizes cover the huge majority of utility, cargo, boat and equipment trailers:
- ST175/80R13 — light utility and small boat trailers
- ST205/75R14 — mid-size single-axle trailers
- ST205/75R15 — the workhorse: utility, landscape, small enclosed
- ST225/75R15 — heavier tandem-axle utility and car haulers
- ST235/80R16 — heavy equipment, gooseneck, large enclosed trailers
Why "ST" is not optional
ST tires use stiffer sidewalls and different rubber compounds than passenger (P) or light-truck (LT) tires. They're built to take vertical load and side-scrub in tandem configurations, not to grip like a drive tire. Putting passenger tires on a trailer axle is the classic cause of highway blowouts.
How to confirm the right size
- Read the trailer's VIN/certification plate (usually on the tongue or frame) — it lists the original size AND required load range.
- Match or exceed the plate. Never go down in load range.
- If the plate is missing, match what's currently mounted and verify total tire capacity exceeds the trailer's GVWR — our trailer load calculator does the math.
Product fitment, load capacity, pressure, and application must always be verified against the trailer, wheel, and tire manufacturer specifications.
Buying for a shop, dealership, or trailer plant? Browse ST trailer tires in stock in Dallas or request wholesale pricing — most quotes answered within one business day.