[TireFitLab](https://tirefitlab.com/) ›
[Tire & wheel reference guides](https://tirefitlab.com/learn/) ›
Tire type guide — P, LT, metric, radial & flotation

# 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](https://tirefitlab.com/tire-size-calculator/). |

[Tire & wheel reference guides](https://tirefitlab.com/learn/) · [Tire load index chart](https://tirefitlab.com/learn/load-index/) · [Tire speed rating chart](https://tirefitlab.com/learn/speed-rating/) · [Plus sizing guide](https://tirefitlab.com/learn/plus-sizing/)

Seasonal check

## Planning a long summer drive?

Use the budget and running-cost tools before a trip, especially if the current tires are worn or the replacement size changes diameter.

[Estimate tire budget](https://tirefitlab.com/tire-budget-calculator/)

## More in this topic: Size validation

Decode markings, compare sizes, and understand diameter, load and speed changes.

- [**How to read a tire size** How to read a tire size: decode every number and letter in P205/55R16 91V — width, aspect ratio, rim diameter, load index, speed rating.](https://tirefitlab.com/learn/how-to-read-tire-size/)
- [**Tire sidewall markings decoder** Complete guide to every marking on a tire sidewall: size string, construction code, load index, speed rating, DOT date, M+S, 3PMSF snowflake, UTQG, max pressure, country of manufacture, and brand-specific symbols.](https://tirefitlab.com/learn/tyre-sidewall-markings/)
- [**Tire load index chart** Use the tire load index chart to convert ratings 60–130 into kg and lb, then verify the vehicle placard and axle-load requirements.](https://tirefitlab.com/learn/load-index/)
- [**Tire speed rating chart** Use the tire speed rating chart to convert symbols from L to Y/ZR into km/h and mph for replacement tire checks.](https://tirefitlab.com/learn/speed-rating/)

### Useful tools

[Tire size converter (mm ↔ inches)](https://tirefitlab.com/tire-size-converter/)[Tire size calculator](https://tirefitlab.com/tire-size-calculator/)

### Technical check

2026-06-28

### Content updated

2026-06-21

What changed

- Checked generated routes, metadata, sitemap inclusion and localized page rendering.
[Methodology](https://tirefitlab.com/methodology/)