ClarityHow to use this tool
- Enter original tire width, original tire aspect ratio, original tire rim diameter, replacement tire width, replacement tire aspect ratio, replacement tire rim diameter, indicated speed.
- Select Calculate to view the result.
- Check the method and assumptions below before using the result.
The method, explained
Sidewall = width × aspect ratio/100. Diameter = 2 × sidewall + rim inches × 25.4 mm. Circumference = π × diameter. Theoretical actual speed = indicated speed × replacement diameter/original diameter.
Using original tire width = 205 mm, original tire aspect ratio = 55 %, original tire rim diameter = 16 in, replacement tire width = 215 mm, replacement tire aspect ratio = 55 %, replacement tire rim diameter = 16 in, indicated speed = 60 mph or km/h, the result is 1.74078177 %. Change these example inputs to match your task; use the method above to check each step.
What to keep in mind
Nominal unloaded dimensions. Actual rolling circumference depends on tire construction, pressure, load and wear. Confirm approved fitment with the vehicle and tire specifications. Planning arithmetic based on your inputs. It does not include live traffic, road restrictions, fares or service availability.
Common questions
How do I read 205/55 R16?
205 is nominal section width in millimeters, 55 means sidewall height is 55% of that width, and 16 is rim diameter in inches. R describes radial construction and is not entered as a number.
Does similar diameter mean the replacement fits?
No. Clearance, wheel width, load and speed ratings, vehicle systems and manufacturer approvals also matter. This calculator compares nominal geometry only.
Methodology maintained by ClarityKit. How these tools are built and checked.