Worked example: Tire Size Calculator
Identical tires. This fixed reference example shows one complete scenario; the interactive results above use your current inputs.
View the example inputs
- Section width
- 205 mm
- Aspect ratio
- 55 %
- Rim diameter
- 16 in
- Comparison width
- 205 mm
- Comparison aspect ratio
- 55 %
- Comparison rim diameter
- 16 in
- Indicated speed
- 100 km/h
| Calculated quantity | Example result |
|---|---|
| Original nominal diameter | 631.9 mm |
| Comparison nominal diameter | 631.9 mm |
| Original nominal circumference | 1,985.1724 mm |
| Diameter change | 0 % |
| Theoretical actual speed | 100 km/h |
Reading a vehicle or travel estimate
Check units and comparison conditions
Fuel consumption in liters per 100 kilometers and economy in miles per gallon move in opposite directions as efficiency improves. US and imperial gallons also have different volumes. A distance, fuel quantity and unit price must describe the same trip before calculating a meaningful cost.
Nominal tire dimensions, torque-based shaft power and loan financing each model a different part of vehicle ownership. A mathematical equivalence does not prove fitment, measured engine output or a lender-approved payment.
Keep variable prices and operating conditions explicit
Fuel prices, actual consumption, lender terms and reimbursement rules can change. Use entered quotes or the supported rule period rather than treating the example values as current local data.
Compare like-for-like trips and vehicles, and read the page’s scope before using the result. The worked example checks the arithmetic; it does not account for every driving condition, maintenance expense or contract provision.
Formula and calculation method
Diameter(mm)=rim(in)×25.4+2×width(mm)×aspect/100. Actual speed=indicated speed×new diameter/original diameter.
Nominal unloaded geometry only; tire load, wear, construction and inflation change rolling circumference. Fitment, clearances and load/speed ratings require separate checks.
Reference Sources
Frequently asked questions
How does this calculator work?
Diameter(mm)=rim(in)×25.4+2×width(mm)×aspect/100. Actual speed=indicated speed×new diameter/original diameter.
What assumptions should I check?
Nominal unloaded geometry only; tire load, wear, construction and inflation change rolling circumference. Fitment, clearances and load/speed ratings require separate checks.
Can I save or print this calculation?
Use Copy link with inputs to reproduce the scenario, Download results for a text record, or Print. Where a schedule is shown, its CSV download includes every row.