Tire & wheel comparison
Tire size calculator
Compare two tire sizes, speedometer estimates, and ride height. Add wheel details to compare position. Vehicle fitment requires separate checks.
Enter your setups
Example tire sizes shown. Replace with your sizes.
Where do I find these numbers?
Read the tire sidewall: 225 is width in millimeters, 45 is sidewall height as a percentage of width, and R17 is a 17-inch rim. Check the vehicle placard for its required original specification. P, LT, ST, load and speed markings are not compatibility checks and are ignored for dimensions. Metric inputs support 145–355 mm, profiles 20–85 in steps of 5, and 13–24-inch rims plus 16.5, 17.5, 19.5 and 22.5-inch LT and commercial rims. Flotation inputs support 24–50-inch diameter and 7–18-inch width.
Optional wheel details
Only needed for position changes. ET is the signed offset stamped on the wheel or listed in its specifications.
Result units
Inputs use standard tire and wheel notation. Result units apply to all derived distances and speeds.
See what changes
Nominal tire dimensions
Current 24.97 in → Proposed 25.72 in overall diameter
Diameter change
+2.98%
+0.74 in
Ride height
+0.37 in
Estimated from radius change
Section width
+0.79 in
Nominal width change
Estimated actual speed
61.8 mph
At indicated 60 mph
Speed assumes the speedometer was accurate with the current tires. Uses diameter ratio.
Vehicle compatibility not checked
A close diameter match does not establish clearance or compatibility. The 3% comparison band is not a vehicle allowance. AWD and staggered setups require manufacturer-specific guidance.
How the setup changes
Proposed is 0.74 in taller overall.
Shared center and scale. Circles compare diameter and rim size, not loaded ride height.
Speedometer
Indicated vs actual
| Dash reads | Estimated speed |
|---|---|
| 30.00 mph | 30.89 mph |
| 60.00 mph | 61.79 mph |
| 70.00 mph | 72.09 mph |
Assumes the speedometer was accurate with the current tires. Uses diameter ratio.
Wheel position not calculated
Add actual wheel details or confirm the same wheels to estimate inner and outer movement.
Detailed comparison
Changes are proposed minus current. Nominal rev/mile uses geometric circumference, not measured rolling circumference. Values round independently; rounded columns may not subtract exactly. Wheel specifications retain industry notation.
| Measurement | Current | Proposed | Change |
|---|---|---|---|
| Tire size | 225/45R17 | 245/40R18 | — |
| Nominal section width | 8.86 in | 9.65 in | +0.79 in |
| Rim diameter | 17 in | 18 in | +1.00 in |
| Overall diameter | 24.97 in | 25.72 in | +0.74 in |
| Radial sidewall estimate | 3.99 in | 3.86 in | -0.13 in |
| Geometric circumference | 78.45 in | 80.79 in | +2.34 in |
| Revolutions per mile | 808 (nominal) | 784 (nominal) | -23 |
| Diameter change | — | — | +2.98% |
| Ride-height estimate | — | — | +0.37 in |
Physical checks still matter
These checks remain unverified:
- Approved rim-width range for the exact tire model
- Load index and speed rating equal to or greater than vehicle requirements
- Brake-caliper, hub, and wheel-fastener compatibility
- Fender, liner, suspension, and full-lock steering clearance
- Clearance at full compression and under expected load
- Alignment, tire pressure, and manufacturer guidance
- Professional inspection when variance or clearance is uncertain
These results compare nominal dimensions. They do not confirm vehicle fitment. Actual clearance varies by tire model, approved rim width, wheel construction, suspension, alignment, body tolerances, steering angle, load, and brake geometry. Verify load and speed ratings and physically test-fit the complete setup before driving.
Diameter change +2.98 percent. Wheel position not calculated. Vehicle compatibility not checked.
Published examples
Explore tire-size comparisons
Each page explains a nominal size change and opens directly in the calculator. Dimensions are checked; vehicle compatibility is not.
Find the right starting point
Look up a size in inches and millimeters, or explore a reviewed comparison before entering your own setup.