Goodyear Endurance Trailer Tire Speed Rating: How to Verify the Limit

The short answer on the Endurance speed limit

The Goodyear Endurance is an ST (Special Trailer) radial that Goodyear rates N, meaning the tire qualified for speeds up to 87 mph while properly inflated and carrying no more than its rated load. Treat that number as a ceiling, not a target. Your actual safe towing speed is the lowest of several limits: the tire's speed rating, the ratings of the trailer wheels, axles and hubs, the tow vehicle manufacturer's towing guidance, and posted legal limits, which in many states set lower maximums for vehicles pulling trailers.

To verify the rating, look at the sidewall rather than relying on the product name. The speed symbol is the letter that follows the load index after the tire size. If a tire on your trailer shows no speed symbol at all, the long-standing industry convention for ST tires is to assume a 65 mph maximum. Do not assume an Endurance rating for tires you have not physically checked, including the spare or tires that came with a used trailer.

How a trailer tire speed rating works

A speed rating comes from a laboratory test in which the tire runs against a drum at a specified load and inflation pressure while speed is stepped up and held for set intervals. What the test really measures is the tire's ability to manage heat. Every rotation flexes the sidewalls and tread, and that flexing generates heat in the rubber, cords and belts. The faster the tire turns, the more flex cycles per minute and the more heat builds up. A tire that passes at the N level has shown it can hold together under those test conditions.

ST tires use stiffer construction to carry heavy loads and resist trailer sway, and they often run for hours near their load limit. Low inflation or excess weight increases sidewall flex, so a tire that is comfortable at highway speed when correctly inflated can overheat at the same speed when it is soft or overloaded. That is why the speed rating, the load index and the inflation pressure have to be read together; the speed figure assumes the other two are being respected.

What changes the answer

Load and pressure come first. An ST tire's load capacity depends on its inflation, and load ranges C, D and E carry different maximum cold pressures. The trailer's certification label, which serves as the trailer's equivalent of a vehicle placard and is usually mounted near the front of the trailer on the left side, lists the original tire size and recommended cold inflation pressure. Many trailer tire makers advise running ST tires at the maximum cold pressure molded on the sidewall to achieve full rated capacity. If the label, the sidewall and Goodyear's guidance for your size do not agree, resolve that with a tire professional before a heavy trip.

Other components can set a lower limit than the tire. Trailer wheels carry their own load and pressure ratings, and the wheel's maximum pressure must be at least as high as the pressure the tire needs. Bearings, axles and older hubs may not be designed for sustained high speed. If tires on the trailer are mixed models, the lowest rating governs the whole setup. Trailers have no drivetrain, so the drivetrain compatibility rules that matter on four-wheel-drive tow vehicles do not apply here, but tires on the same axle or tandem set should still match in size, construction and load range so each one carries its share of the weight.

Operating conditions also matter. High ambient temperatures, hot pavement, long uninterrupted runs and loads near the maximum all push tires closer to their thermal limit. Age is another factor: rubber compounds degrade over time even when tread depth looks fine, so an older tire may not perform the way it did when new, regardless of the letter on the sidewall.

What the owner can do

Start with a sidewall check on every tire, including the spare. Record the tire size, the load index (ST tires may show two numbers for single and dual mounting), the speed symbol, the load range, the maximum load and maximum cold pressure, and the DOT date code, whose last four digits give the week and year of manufacture. Compare those details with the trailer certification label and with the ratings stamped on the wheels.

Weigh the loaded trailer at a public scale and compare each axle's weight with the combined capacity of the tires on that axle, leaving a margin rather than running at the limit. Check inflation pressure with a gauge before each trip while the tires are cold; trailer tires can look normal while seriously underinflated. Inspect the tread and sidewalls for bulges, cracks, cuts and uneven wear, and measure tread depth at several points across the tread, since irregular wear can signal alignment, axle or loading problems.

On the road, choose a cruising speed with clear margin below the lowest applicable limit, especially in hot weather or with a full load. At stops, walk around the trailer and look for changes in tire shape or pressure, and compare tire and hub temperatures with an infrared thermometer if you carry one; one tire running noticeably hotter than its neighbors deserves attention before you continue.

Limitations and next step

This guide cannot confirm the rating of a specific tire in your possession. Product lines change over time, and individual sizes or production runs may be marked differently, so the sidewall and Goodyear's current data for your exact size are the authority. General conventions such as the 65 mph default for unmarked ST tires are a fallback, not a substitute for the actual marking.

Get help from a tire shop or trailer dealer if the certification label is missing or unreadable, if the trailer has been modified or rebuilt, if you are changing load range or wheel size, or if a tire has suffered a blowout, impact or sustained low-pressure running. In those cases the correct size, load capacity and pressure depend on details that only an inspection of your trailer can establish.