The three numbers do different jobs
Width is a nominal dimension, not an exact installed measurement. The aspect ratio is a percentage: a 45-series sidewall changes height when width changes. The last number must match the wheel’s rim diameter.
Load index and speed rating usually follow the size. Extra-load, load-range, run-flat and automaker-specific markings add information. Record the full description rather than only the headline numbers.
Use the vehicle label as your starting point
An existing tire may be an aftermarket change, so copying its sidewall is not always enough. Check your vehicle’s label and manual, and read both axles on a staggered setup.
Our calculator explains nominal dimensions. It does not assess clearance, load, wheel width or vehicle approval. Have a professional confirm the replacement before installation.
Common questions
Does R mean radius?
No. R identifies radial construction.
Sources & further reading
Manufacturer information can change. Confirm the exact product and vehicle specification before ordering.