What Is Compare Tires?
Compare Tires is a tire comparison tool for evaluating two or more tire sizes by their key dimensions. Also called tire comparison, it helps you understand how changing from one tire size to another may affect tire width, sidewall height, overall diameter, circumference, and rotational speed.
The tool is useful when checking a replacement tire size or evaluating a different tire package for a target vehicle. It provides dimensional information, but it does not by itself confirm complete vehicle fitment.
How Tire Comparison Works
A tire size such as 225/45R17 contains several measurements:
- 225 is the nominal section width in millimeters.
- 45 is the aspect ratio, expressed as a percentage of the tire’s width. The sidewall height is approximately 45% of 225 mm.
- R identifies radial construction.
- 17 is the wheel diameter in inches that the tire is designed to fit.
A comparison calculator uses these values to estimate and compare:
- Tire section width
- Sidewall height
- Overall tire diameter
- Rolling circumference
- Difference in diameter and circumference
- Approximate revolutions per mile or kilometer
- Percentage change from the reference tire
These measurements are normally nominal. The actual dimensions can vary by tire model, tread design, approved measuring rim, inflation pressure, and load.
Why Compare Tires Matters for Fitment
Changing tire dimensions can affect more than appearance. A wider tire may need additional clearance from the suspension, inner wheel well, or fender. A taller tire can reduce clearance above the tire and may alter the effective gearing and speedometer reading. A shorter tire may provide more clearance but can reduce ground clearance and change the vehicle’s overall gearing.
Overall diameter is particularly important because it affects how far the vehicle travels with each wheel rotation. If the replacement tire has a different circumference, the indicated vehicle speed and distance may no longer match the original calibration exactly. The percentage difference shown by the calculator helps estimate the size of that change.
Tire comparison should also be considered with the wheel’s wheel diameter, wheel width, and offset. A tire size is not automatically suitable for every wheel with the same diameter. The wheel must have an appropriate width range, and the complete tire-and-wheel assembly must clear the vehicle’s brakes, suspension, and bodywork.
Example of a Tire Comparison
Consider a comparison between 225/45R17 and 235/45R17:
- Both tires are intended for a 17-inch wheel.
- The second tire is nominally 10 mm wider.
- The approximate sidewall height increases from 101.3 mm to 105.8 mm.
- The approximate overall diameter increases from 634 mm to 643 mm.
- The second tire is approximately 1.4% taller in diameter.
This indicates a dimensional change, not a guaranteed fitment result. The wider tire may require a different wheel width or additional clearance, and the vehicle’s recommended load rating, speed rating, and tire approval requirements must also be checked.
What Compare Tires Does Not Confirm
A tire comparison tool generally does not determine all of the following:
- Whether the tire clears the vehicle’s suspension or fenders
- Whether the tire is approved for the selected wheel width
- Whether the wheel has the correct bolt pattern / PCD
- Whether the wheel center bore matches the vehicle hub
- Whether the wheel offset provides suitable inner and outer clearance
- Whether brake clearance is sufficient
- Whether the tire’s load index and speed rating are appropriate
Bolt pattern, center bore, and wheel offset are wheel-fitment measurements rather than tire-size measurements. A tire can have suitable dimensions while the wheel carrying it is incompatible with the vehicle.
Common Tire Comparison Mistakes
- Treating the displayed overall diameter as an exact measurement for every tire model.
- Assuming the same wheel diameter means two tire sizes are interchangeable.
- Ignoring the approved wheel-width range.
- Comparing width alone without checking sidewall height and overall diameter.
- Assuming a small percentage difference guarantees adequate physical clearance.
- Forgetting to check load index, speed rating, vehicle configuration, and local requirements.
Use Compare Tires as a dimensional screening tool. Before changing tire size, verify the tire manufacturer’s specifications and assess the complete wheel-and-tire package on the target vehicle. The result may support a Direct Fit assessment, but dimensional comparison alone may still require Check Fitment.