Diâmetro Pneu (LT/P)

Tire diameter (LT/P designation)

A modern tire marking like 205/55R16 packs three numbers into a string. 205 is the section width in millimeters. 55 is the aspect ratio, the sidewall height as a percentage of the width. R flags radial construction, and 16 is the rim diameter in inches. From there the overall diameter is D = 2·(width·aspect/100) + rim·25.4 (in mm). LT (Light Truck) and P (Passenger) sizes use the very same rule; the prefix only sets the load and pressure spec, not the geometry.

Why it matters: changing tire diameter changes the effective rolling circumference, which makes the speedometer and odometer read incorrectly. Common designation prefixes are P (Passenger), LT (Light Truck), C (Commercial van) and ST (Special Trailer). Speed ratings sit at the end of the marking: Q = 160 km/h, V = 240, Y = 300, ZR > 240 km/h.

Real-world applications

Used when replacing tires (keep the overall diameter within roughly ±3% of the OEM size to preserve speedometer accuracy and ABS calibration), planning a rim upsize (lower aspect ratio to compensate for the larger rim, keeping total height), tuning, and off-road builds where a larger diameter buys ground clearance but forces speedometer recalibration and may change the gear ratio behavior.

FAQ

What is the "profile" or aspect ratio? It is the sidewall height expressed as a percentage of the section width. A 55-series tire has a sidewall equal to 55% of the width.

Can I mix LT and P on the same car? Not recommended. LT tires have stiffer sidewalls and higher load indices for trucks; P tires give a more comfortable ride and are calibrated for passenger cars.

How much diameter change is safe? A common rule of thumb is ±3%. Beyond that, the speedometer error grows, and the ABS/ESC may need recalibration.