Tire Tools
Tire dimensions, comparisons and speed.
Methodology & limits
Read the size. Understand the change.
From the numbers on the sidewall to a side-by-side comparison. Start with a tire size, then see what changes in diameter, width, and estimated speed.
Tire markings describe nominal geometry. Manufacturer specifications and real measurements may differ. Read the methodology and limits.
How to read a tire size
In 225/45R17, 225 is the nominal section width in millimeters, 45 is the sidewall height as a percentage of that width, and 17 is the wheel diameter in inches. The letter R describes radial construction.
For this size, the nominal sidewall is 101.25 mm and the nominal diameter is 634.3 mm. The theoretical circumference is approximately 1,992.7 mm.
Metric and flotation formats
The tools also support sizes such as 33x12.50R15. Here, 33 is the nominal overall diameter in inches and 12.50 is the nominal section width in inches. Changing the display units does not change the meaning of either notation.
Where to start
Start with one tire size. Compare your replacement, then estimate the speed change.