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Calculadora de medida de neumático

Introduce la medida original y la nueva. Obtén el cambio de diámetro y el error del velocímetro.

Calcular

Measurements convert when you switch units

mm
%
in
mm
%
in
km/h

Updates as you type

Resultado

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La fórmula

Diámetro = llanta×25,4 + 2×(ancho×perfil/100). Velocidad real ≈ indicada × (Ø_nuevo ÷ Ø_original).

Ø mm = rim_in × 25.4 + 2 × (width_mm × aspect ÷ 100) · Actual speed ≈ Indicated × (Ø_new ÷ Ø_stock)

Ejemplo resuelto

  1. Stock 225/45R17 → Ø = 17×25.4 + 2×(225×0.45) = 634.3 mm
  2. New 245/40R18 → Ø = 18×25.4 + 2×(245×0.40) = 653.2 mm
  3. Ratio 653.2÷634.3 ≈ 1.030 · at 100 indicated → ≈ 103.0 actual

Resultado: +3.0% diameter · ~103 at indicated 100

How tire diameter and speedometer error are calculated

We use the industry metric size code. Real rolling radius also depends on load and inflation; this is the geometric overall diameter.

Size code

225/45R17 means 225 mm section width, 45% aspect (sidewall = 45% of width), R = radial, 17-inch rim. Plus-sizing often raises rim size while lowering aspect to keep diameter close.

Speedometer and odometer

Cars assume the stock circumference. Larger tires mean you travel farther per wheel revolution — actual speed is higher than indicated, and the odometer under-reports distance.

What we do not model

No load deflection, wear, or ABS/ESP calibration limits. Many makers advise staying within about ±3% of stock diameter; check your handbook and local rules.

Datos interesantes

Plus-sizing goal

Moving to a larger rim usually pairs with a lower aspect ratio so overall diameter — and gearing — stay near stock.

Legal and warranty

Some regions restrict tire sizes on the vehicle’s placard. Oversized changes can affect speedometer legality and warranty.

Load index matters

Diameter is not enough — match or exceed the load and speed ratings stamped on the sidewall.

AWD caution

On all-wheel-drive cars, mismatched diameters between axles can stress the driveline.

Preguntas frecuentes

Ø (mm) = rim inches × 25.4 + 2 × (width × aspect/100). Compare stock and new to get the percent change.

Yes. With a larger overall diameter, indicated speed is lower than actual. This tool shows actual speed at your indicated value.

A common rule of thumb is to stay within about 3% of stock diameter, but follow the vehicle maker and tire professional guidance.

Yes — the same circumference factor scales reported distance. Larger tires under-report mileage.

Yes for metric sizes (e.g. 225/45R17). Some light-truck sizes use different notations; convert before using this form.

Referencias

  1. Tire basics — NHTSA U.S. tire safety and labeling context.
  2. Tyre labelling — European Commission EU tyre label framework.