TIREVS.
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How to read a tire size

The 275/60R20 code describes width, sidewall ratio, construction and wheel diameter. Compare it with the vehicle placard and the exact tire model’s specifications.

Where to find your tire size

Check the vehicle placard on the driver’s door or door frame and the owner’s manual for the original requirements. The sidewall shows the tire currently installed; it may differ from the original specification. Check front and rear requirements separately.

Discount Tire — How to check tire size
Workshop photograph of a Sunwide Durevole A/T tire on a Silverado, with the 275/60R20 115T sidewall code visible on the left
Sunwide Durevole A/T · 275/60R20 115T

Installed example with a 275/60R20 115T sidewall code.

Read the code, part by part

Size and construction275/60R20
Service description115T
275Section width
275 mm section width, measured from sidewall to sidewall.
60Aspect ratio
Sidewall height is 60% of width: 275 × 0.60 = 165 mm.
RConstruction
R means radial construction.
20Wheel diameter
20 inches at the bead seat = 508 mm.
115Load index
115 = 1,215 kg rated load per tire under the specified service conditions. Use the vehicle placard for inflation pressure.
TSpeed rating
T = 190 km/h (118 mph) speed category under specified service conditions. Choose road speed for the conditions and applicable limits.
Nominal geometry

Side view

DOverall diameter32.99 in83.80 cm
SSidewall height6.50 in16.50 cm
WDWheel diameter20.00 in50.80 cm

Front view

DOverall diameter32.99 in83.80 cm
WSection width10.83 in27.50 cm
DOverall diameter
32.99 in83.80 cm838.00 mm
WSection width
10.83 in27.50 cm275.00 mm
SSidewall height
6.50 in16.50 cm165.00 mm
WDWheel diameter
20.00 in50.80 cm508.00 mm
CCircumference
103.65 in263.27 cm2,632.65 mm
Photorealistic illustration. Generic tread and wheel; dimensions are calculated from the size code.

Geometry comes from 275/60R20. Match the service description to the tire and vehicle specifications.

275 — section width

The nominal section width is 275 millimeters, measured from sidewall to sidewall under specified conditions. Tread width is a separate measurement; the tire model and measuring wheel affect the published section width.

60 — aspect ratio

The sidewall height is 60% of the nominal section width: 275 × 0.60 = 165 mm. The profile number expresses a percentage.

R — radial construction

R identifies radial construction. ZR may appear in some high-speed size markings and is accepted as an input. Read the speed symbol in the full service description.

20 — wheel diameter

The wheel bead-seat diameter is 20 inches, or 508 mm. Wheel width and offset still need to match the tire and vehicle requirements.

How we calculate it

275 × 60 / 100 = 165.00 mm6.50 in16.50 cm
(20 × 25.4) + (2 × 165) = 838.00 mm32.99 in83.80 cm
π × 838 = 2,632.65 mm103.65 in263.27 cm

Flotation sizes: 35x12.5R17

35 is nominal overall diameter in inches, 12.5 is nominal section width in inches, and 17 is wheel diameter in inches. The nominal sidewall is (35 − 17) / 2 = 9 inches. Use the format printed on the tire and compare the exact model’s published dimensions.

Check load, speed and vehicle requirements

Match the vehicle’s required load and speed ratings to the exact tire model. For LT or P tires, use the vehicle placard and the tire maker’s load and inflation guidance.

In 275/60R20 115T, load index 115 means a rated 1,215 kg per tire, and T is the 190 km/h (118 mph) speed category under the tire manufacturer’s specified service conditions. Check the vehicle placard and the exact tire model’s service data for load, pressure and speed-rating requirements. Choose road speed for the conditions and applicable limits.

Michelin — Load and speed rating tables

Nominal geometry versus real tires

The simple formula describes an unloaded nominal circle. Tread design, measuring rim, manufacturing variation, inflation, wear and load affect real dimensions and rolling circumference. Use the manufacturer’s specification for the exact model before making a purchase.

Sources and limitations

Michelin — How to read a tire size

Compare these dimensions with the tire manufacturer’s published measurements and your vehicle’s tire and wheel specifications.

Compare sizes