Tire type guide — P, LT, metric, radial & flotation
What do the letters in a tire size mean?
The optional prefix shows the vehicle type: P = passenger (P-metric), LT = light truck. No prefix = Euro-metric (same formula, slightly different load deduction). The construction letter R = radial (standard on all modern passenger tires), D = diagonal bias (rare). Flotation/LT sizes use the overall-diameter × section-width format (e.g. 33x10.50R15) instead of the standard width/aspect/rim format.
| Size | Specification |
|---|---|
| P (P-metric) | Passenger-vehicle tire. Same width formula as Euro-metric but 10% lower load capacity vs. an unmarked tire of the same size (US standard). |
| LT (Light Truck) | Light-truck tire. Higher load ratings (Load Range C–F). Some LT sizes use flotation format: OD × section-width × R × rim (e.g. 33x10.50R15LT). |
| Euro-metric (no prefix) | European standard. No prefix = Euro-metric. Same size formula as P-metric but load capacity calculated without the 10% P-metric deduction. |
| R — Radial | Standard on all modern passenger tires. Ply cords run perpendicular to the direction of travel, crossed by a steel belt. |
| D — Diagonal / Bias-ply | Ply cords run at an angle (30–45°) to the direction of travel. Rare on passenger tires; still used on some trailers and off-road applications. |
| Flotation (e.g. 33x12.50R16) | Oversized off-road format: overall diameter × section width × R × rim diameter. Common on lifted trucks and SUVs. TireFitLab supports this format in the calculator. |
Tire & wheel reference guides · Tire load index chart · Tire speed rating chart · Plus sizing guide
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