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Special Trailer (ST) tires stand apart from typical passenger car tires. Engineered with greater stiffness, they support elevated load capacities, sustain higher air pressures, and minimize sidewall flex to curb trailer sway. These tires incorporate reinforced steel belts and heavy-duty wires for superior durability. Additionally, their rubber compounds include enhanced antioxidants to combat degradation from UV exposure, sunlight, and ozone, preventing early dry rot.

In contrast to the softer, compliant sidewalls on car and SUV tires that cushion road imperfections, trailer tires prioritize rigidity. This firmness prevents compression and deflection, allowing them to bear heavy loads without collapsing. Similar to how underinflation generates excess heat, the sturdy build of ST tires promotes cooler operation during extended trips. They also feature shallower tread depths - averaging 8/32 inches compared to 10/32 to 11/32 inches on new passenger tires - which proves advantageous.

Reduced tread depth lowers rolling resistance and limits tread distortion under weight. The contact patch, or the tire portion in road contact, tends to twist during steering and rolling due to vehicle mass. Since trailer tires focus on load-bearing rather than propulsion or direction, their strong sidewalls resist buckling and squirming effectively.

Trailer Tires Feature Unique Sizing

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Though trailer tires boast rigid sidewalls and robust builds, they generally appear in smaller dimensions than passenger (P) or light truck (LT) tires. They often have taller aspect ratios and slimmer widths, optimizing them for demanding towing and hauling tasks. The aspect ratio, one of several sidewall markings, measures sidewall height relative to width. A smaller ratio indicates shorter sidewalls, common in performance-oriented low-profile tires.

Narrower tires with elevated aspect ratios suit trailers well, as their compact contact patches apply greater pressure per square inch for improved straight-line stability under load. Opting for wider tires beyond manufacturer specs can lead to instability, erratic handling, or vibrations that strain the trailer's hitch.

Selecting the Ideal Trailer Tire

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Picking the correct trailer tire mirrors choosing tires for passenger vehicles: prioritize size and load range. Load range, indicated by sidewall letters and numbers, specifies maximum inflation pressure and ply strength. For example, ST tires rated C1 or C2 both equate to 6-ply construction, yet C1 handles 50 psi while C2 maxes at 35 psi.

The load index, another sidewall detail, reveals the tire's peak weight capacity. Higher indices support greater loads; consult a chart for precise figures. A load index of 60 accommodates 551 pounds, whereas 100 manages up to 1,764 pounds.

Speed rating matters too. Conventional ST tires cap at 65 mph, but advanced models offer more. An L rating permits 75 mph, and M reaches 81 mph without sacrificing safety.