Tire Diameter Comparison Calculator

Tire Diameter Comparison is evaluated from Tire 1 - Width, Tire 1 - Aspect Ratio and Tire 1 - Rim Diameter. The calculation reports Tire 1 Diameter, Tire 2 Diameter and Diameter Difference.

Results

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About the Tire Diameter Comparison Calculator

Tire Diameter Comparison is treated here as a quantitative relation between Tire 1 - Width, Tire 1 - Aspect Ratio, Tire 1 - Rim Diameter and Tire 2 - Width and Tire 1 Diameter, Tire 2 Diameter, Diameter Difference and Tire 1 Circumference.

The calculator uses a multi formula configuration. Each reported value is read as a direct evaluation of the stored rules with the declared field formats and units.

Formula basis:
Sidewall height = width x aspect ratio / 100 (in mm). Convert to inches by dividing by 25.4. Diameter = rim + 2 x sidewall. Speedometer error from circumference difference.

Interpret the outputs in the order shown by the result fields. Optional inputs affect only the outputs that depend on those variables.

Formula & How It Works

The calculation applies the following relations exactly as recorded in the metadata:

Sidewall height = width x aspect ratio / 100 (in mm). Convert to inches by dividing by 25.4. Diameter = rim + 2 x sidewall. Speedometer error from circumference difference.

Each output field is produced by substituting the supplied inputs into the relevant relation and then applying the declared rounding or text format.

Worked Examples

Example 1: Stock vs slightly wider: 225/45R17 vs 245/40R18

Inputs

width1: 225 ratio1: 45 rim1: 17 width2: 245 ratio2: 40 rim2: 18
Tire 1 Diameter: 24.972 in. Tire 2 Diameter: 25.717 in. Diameter Difference: 0.744 in. Tire 1 Circumference: 78.453 in. Tire 2 Circumference: 80.791 in. Speedometer Error: 2.98%. Tire 1 Sidewall Height: 3.986 in. Tire 2 Sidewall Height: 3.858 in

With Tire 1 - Width = 225, Tire 1 - Aspect Ratio = 45, Tire 1 - Rim Diameter = 17 and Tire 2 - Width = 245 as the stated inputs, the result is Tire 1 Diameter = 24.972 in, Tire 2 Diameter = 25.717 in and Diameter Difference = 0.744 in. Each value corresponds to the declared output fields.

Example 2: Truck lift: stock vs bigger tires 265/70R17 vs 285/75R16

Inputs

width1: 265 ratio1: 70 rim1: 17 width2: 285 ratio2: 75 rim2: 16
Tire 1 Diameter: 31.606 in. Tire 2 Diameter: 32.831 in. Diameter Difference: 1.224 in. Tire 1 Circumference: 99.294 in. Tire 2 Circumference: 103.141 in. Speedometer Error: 3.87%. Tire 1 Sidewall Height: 7.303 in. Tire 2 Sidewall Height: 8.415 in

With Tire 1 - Width = 265, Tire 1 - Aspect Ratio = 70, Tire 1 - Rim Diameter = 17 and Tire 2 - Width = 285 as the stated inputs, the result is Tire 1 Diameter = 31.606 in, Tire 2 Diameter = 32.831 in and Diameter Difference = 1.224 in. Each value corresponds to the declared output fields.

Example 3: Same size comparison (no change): 205/55R16 vs 205/55R16

Inputs

width1: 205 ratio1: 55 rim1: 16 width2: 205 ratio2: 55 rim2: 16
Tire 1 Diameter: 24.878 in. Tire 2 Diameter: 24.878 in. Diameter Difference: 0 in. Tire 1 Circumference: 78.156 in. Tire 2 Circumference: 78.156 in. Speedometer Error: 0%. Tire 1 Sidewall Height: 4.439 in. Tire 2 Sidewall Height: 4.439 in

With Tire 1 - Width = 205, Tire 1 - Aspect Ratio = 55, Tire 1 - Rim Diameter = 16 and Tire 2 - Width = 205 as the stated inputs, the result is Tire 1 Diameter = 24.878 in, Tire 2 Diameter = 24.878 in and Diameter Difference = 0 in. Each value corresponds to the declared output fields.

Example 4: SUV winter swap: 235/65R17 (summer) vs 225/65R17 (winter)

Inputs

width1: 235 ratio1: 65 rim1: 17 width2: 225 ratio2: 65 rim2: 17
Tire 1 Diameter: 29.028 in. Tire 2 Diameter: 28.516 in. Diameter Difference: -0.512 in. Tire 1 Circumference: 91.193 in. Tire 2 Circumference: 89.585 in. Speedometer Error: -1.76%. Tire 1 Sidewall Height: 6.014 in. Tire 2 Sidewall Height: 5.758 in

With Tire 1 - Width = 235, Tire 1 - Aspect Ratio = 65, Tire 1 - Rim Diameter = 17 and Tire 2 - Width = 225 as the stated inputs, the result is Tire 1 Diameter = 29.028 in, Tire 2 Diameter = 28.516 in and Diameter Difference = -0.512 in. Each value corresponds to the declared output fields.

Common Use Cases

  • Compare two tire sizes for diameter difference
  • Calculate speedometer error after changing tire size
  • Find sidewall height from tire size notation