Hi-Run Trailer Tire Speed Rating
Hi-Run trailer tires carry a speed rating that tells owners the maximum sustained road speed the tire is designed to handle under its rated load and inflation pressure. The rating appears as a letter code near the tire size and load index on the sidewall, and it matters because trailer heat buildup rises sharply with speed. Matching that letter to your towing conditions helps prevent premature tread separation and casing damage, especially when a trailer is loaded near its gross vehicle weight rating.
Essential answer
The Hi-Run trailer tire speed rating is the letter designation molded into the sidewall that identifies the tire's maximum speed capability under controlled test conditions. It is not a recommendation to drive that fast in every situation, but rather a ceiling for sustained operation when the tire is properly inflated and carrying its rated load. Because no confirmed specification was supplied for a specific Hi-Run model in this material, the exact letter for a given tire must be read from the sidewall and compared with the trailer manufacturer's vehicle placard before towing.
Speed rating works together with load index and inflation pressure rather than as an isolated number. A trailer tire may be marked for a common highway rating such as L, M, or N depending on construction and intended service, but the safe operating speed can be lower when the axle is heavily loaded, tire pressure is below the cold inflation target, or ambient temperatures are high. Trailer owners should treat the sidewall letter as one part of a broader load-speed-pressure relationship that protects the casing from excessive heat.