Trailer Tire Size Chart &
Load Capacity Calculator
Verify your travel trailer, camper, boat, or equipment trailer tire safety. Calculate axle capacity, target cold PSI by Load Range (C, D, E, F), and ensure an optimal 15–20% safety reserve margin to prevent highway blowouts.
Trailer tongue weight is supported by your truck's hitch, reducing the direct weight carried by the trailer tires.
SAFE FOR HIGHWAY TOWING (41.7% RESERVE MARGIN)
ST vs. Passenger (P) vs. Light Truck (LT) Tires
Why passenger car tires must never be mounted on travel trailers and how dedicated ST radial tires prevent trailer sway.
| Feature / Spec | Special Trailer (ST) | Passenger Car (P-Metric) | Light Truck (LT) |
|---|---|---|---|
| Sidewall Construction | Heavier steel/polyester plies (Stiff) | Thin & Flexible (Engineered for ride comfort) | Reinforced (Medium-Stiff) |
| Anti-Sway Stability | Maximum (Resists trailer fishtailing) | Severe Sway Danger (Dangerous flex) | Moderate Stability |
| Inflation Pressure (Cold) | 50, 65, 80, or 110 PSI (Fixed) | 32 to 36 PSI | 50 to 80 PSI |
| UV & Ozone Protection | High antiozonants (Resists storage aging) | Standard (Requires constant driving) | Standard Commercial |
| Tread Depth & Heat | Shallow (8-10/32") to run cooler | Standard (10-11/32") | Deep (14-17/32" runs hotter) |
| Trailer Suitability | 100% Recommended | NEVER USE ON TRAILERS | Heavy Fifth Wheels Only (16") |
50 PSI
6-Ply EquivalentStandard for small boat trailers, lightweight utility trailers, and pop-up tent campers (13" & 14" wheels).
65 PSI
8-Ply EquivalentStandard OEM on mid-size travel trailers (20–26 ft) and dual-axle boat trailers (ST205/75R14 and ST205/75R15).
80 PSI
10-Ply EquivalentThe gold standard for heavy travel trailers, RVs, and fifth wheels. Upgrading from D to E prevents blowouts.
95 - 110 PSI
12 to 14-Ply EquivalentHigh-pressure commercial application for heavy goosenecks, dump trailers, and tri-axle toy haulers (16" wheels).
Master Special Trailer (ST) Tire Size Directory
Complete technical specs: diameter, section width, ply rating, max load in lbs/kg, and speed rating.
| Tire Size | Rim | Dimensions | Load Range | Max Load (Lbs / Kg) | Cold PSI | Speed Rating | Common Applications |
|---|---|---|---|---|---|---|---|
| ST175/80R13 | 13" | 24.0" × 7.0" | Range C (6-Ply) | 1360 lbs (617 kg) | 50 PSI | M (81 mph) | Light Utility / Small Boat |
| ST175/80R13 | 13" | 24.0" × 7.0" | Range D (8-Ply) | 1610 lbs (730 kg) | 65 PSI | M (81 mph) | Light Utility / Small Boat |
| ST205/75R14 | 14" | 26.1" × 8.0" | Range C (6-Ply) | 1760 lbs (798 kg) | 50 PSI | M (81 mph) | Boat / Single Axle Travel Trailer |
| ST205/75R14 | 14" | 26.1" × 8.0" | Range D (8-Ply) | 2040 lbs (925 kg) | 65 PSI | M (81 mph) | Boat / Single Axle Travel Trailer |
| ST215/75R14 | 14" | 26.7" × 8.5" | Range C (6-Ply) | 1870 lbs (848 kg) | 50 PSI | M (81 mph) | Campers / Cargo Hauler |
| ST205/75R15 | 15" | 27.1" × 8.0" | Range C (6-Ply) | 1820 lbs (826 kg) | 50 PSI | M (81 mph) | Pop-Up Camper / Light Travel Trailer |
| ST205/75R15 | 15" | 27.1" × 8.0" | Range D (8-Ply) | 2150 lbs (975 kg) | 65 PSI | M (81 mph) | Travel Trailer / Tandem Boat |
| ST225/75R15 | 15" | 28.3" × 8.8" | Range D (8-Ply) | 2540 lbs (1152 kg) | 65 PSI | M (81 mph) | Most Popular Travel Trailer OEM |
| ST225/75R15 | 15" | 28.3" × 8.8" | Range E (10-Ply) | 2830 lbs (1284 kg) | 80 PSI | M (81 mph) | Heavy Travel Trailer Upgrade (Endurance) |
| ST235/80R16 | 16" | 30.8" × 9.3" | Range E (10-Ply) | 3520 lbs (1597 kg) | 80 PSI | M (81 mph) | Standard Fifth Wheel / Toy Hauler |
| ST235/80R16 | 16" | 30.8" × 9.3" | Range F (12-Ply) | 3960 lbs (1796 kg) | 95 PSI | L (75 mph) | Heavy Equipment / Horse Trailer |
| ST235/85R16 | 16" | 31.7" × 9.3" | Range E (10-Ply) | 3640 lbs (1651 kg) | 80 PSI | M (81 mph) | Commercial Cargo / Tall Fifth Wheel |
| ST235/85R16 | 16" | 31.7" × 9.3" | Range F (12-Ply) | 3960 lbs (1796 kg) | 95 PSI | L (75 mph) | Heavy Dump / Gooseneck |
| ST235/85R16 | 16" | 31.7" × 9.3" | Range G (14-Ply) | 4400 lbs (1996 kg) | 110 PSI | L (75 mph) | Maximum Commercial Capacity (14-Ply) |
Frequently Asked Questions: Special Trailer (ST) Tires
Can I put passenger car (P-Metric) tires on a trailer?▼
No, absolutely not. Passenger (P-Metric) tires have thin, flexible sidewalls engineered for passenger ride comfort. On a trailer, this sidewall flex dramatically increases lateral sway (fishtailing), leading to dangerous loss of vehicle control. Furthermore, passenger tires must be derated by roughly 9-10% of their load capacity when used on a trailer under federal safety standards (TRA and FMVSS).
What is the difference between ST and LT trailer tires?▼
Special Trailer (ST) tires are built with stiffer sidewalls, heavier polyester/steel plies, and shallower tread to dissipate heat and prevent trailer sway. They also contain higher concentrations of UV and ozone inhibitors to resist weather checking during long storage periods. Light Truck (LT) tires are sometimes used on heavy fifth wheels (16-inch rims), but standard ST radial tires remain the gold standard for dedicated trailer stability.
What tire pressure should I run in trailer tires?▼
Trailer tires should ALWAYS be inflated to their maximum cold inflation pressure listed on the sidewall: 50 PSI for Load Range C (6-ply), 65 PSI for Load Range D (8-ply), 80 PSI for Load Range E (10-ply), and 95-110 PSI for Load Range F/G. Never lower trailer tire pressure for a 'softer ride'; underinflation is the leading cause of trailer tire blowouts on the highway due to excessive heat buildup.
What is the speed rating limit on ST trailer tires?▼
Historically, all ST trailer tires were limited by DOT standards to 65 MPH (104 km/h). However, modern premium ST radial tires feature speed rating symbols stamped on the sidewall: 'L' is rated for 75 MPH (120 km/h), 'M' is rated for 81 MPH (130 km/h) (common on Goodyear Endurance and Carlisle Radial Trail HD), and 'N' is rated for 87 MPH (140 km/h). If no speed letter is present, the tire must not exceed 65 MPH.
How often should trailer tires be replaced?▼
Trailer tires should typically be replaced every 4 to 6 years regardless of remaining tread depth. Trailer tires rarely wear out their tread; instead, they age out from internal rubber oxidation and UV degradation. Inspect the 4-digit DOT date code stamped on the sidewall (e.g., '2422' means the 24th week of 2022).