Why Trailer Tires Blow Out on the Highway (And How to Spec Against It)
Trailer tires usually fail from heat, not punctures. Underinflation, running at 100% of rated load, and rubber age all build heat until the casing lets go — typically at highway speed in summer. Speccing tires with about 20% reserve capacity and checking cold pressure before every trip prevents most blowouts.
Heat is the killer
A trailer tire almost never "just blows." It overheats. Three things build that heat:
| Cause | Why it builds heat | The fix |
|---|---|---|
| Underinflation | sidewall flexes more per revolution | check cold PSI before every trip |
| No capacity reserve | tire runs at 100% of rated load | spec ~20% headroom |
| Age | old rubber flexes poorly, cracks internally | replace ST tires around 5–6 years |
The 20% reserve rule
Add up your tires' rated capacity and compare it to your trailer's real loaded weight. If the load uses more than about 80% of total capacity, you have no thermal headroom — and summer highway miles will find that out.
Run your numbers in the trailer tire load calculator: GVWR, axles, hitch type in — the per-tire capacity and load index you need out, reserve included.
Pressure: the daily discipline
ST tires carry their rated load only at the maximum pressure molded on the sidewall. And pressure follows temperature — air set in a warm garage reads several PSI lower on a cold morning (see exactly how much). Check cold, before driving.
Age: the invisible failure
Trailer tires age out before they wear out — sun and sitting do more damage than miles. Decode your manufacture date with the DOT date decoder; most trailer tire guidance says replace around 5–6 years regardless of tread.