Tire Size Decoder and Comparison
Decode one tire size, then optionally compare a second code without switching tools.
Decode the first tire
Enter width, aspect ratio, construction, and rim as one code. The result separates each component and calculates sidewall-based diameter and circumference.
Add a comparison only when needed
The second code is optional. When present, the same calculation compares diameter, circumference, and the geometric speed ratio.
Example: 205/55R16 and 225/45R17
The codes use different widths and rims but produce close overall diameters. The exact values help quantify the difference; they do not certify compatibility.
Geometry is not fitment
Check rim width, clearance, load and speed rating, vehicle systems, manufacturer documentation, and applicable approval before changing tires.
Frequently Asked Questions
What does 205/55 R16 mean?
205 is nominal width in millimetres, 55 is sidewall height as a percentage of width, R means radial construction, and 16 is rim diameter in inches.
How is overall tire diameter calculated?
The model doubles sidewall height and adds rim diameter converted from inches to millimetres.
How does tire size affect the speedometer?
A different rolling diameter changes distance per revolution. The comparison shows a geometric actual-speed ratio at an indicated 100, without modeling vehicle calibration.
Does a similar diameter mean the tire fits the same rim?
No. Rim width, bead profile, clearance, manufacturer specifications, and vehicle requirements are separate from rim diameter.
Are load and speed indexes decoded?
The parser can preserve an optional index suffix but does not interpret it. Verify both indexes against current tire and vehicle documentation.
Why can approval still be required?
Similar circumference alone does not prove clearance, handling, braking, load capacity, system compatibility, or legal approval.
What does a DOT number mean?
DOT markings contain manufacturing and identification information, including a date code. They are not part of the size expression decoded here.
Does the code prove the tire fits my vehicle?
No. Use the vehicle and wheel specifications and obtain qualified confirmation before changing sizes.