Use our tire size comparison calculator to compare two tire sizes by width, sidewall height, overall diameter, circumference, revolutions per mile, ride height, and estimated speedometer difference.
Current Tire Size
New Tire Size
Size Comparison
| Measurement | Current Tire | New Tire | Difference |
|---|---|---|---|
| Width | |||
| Sidewall Height | |||
| Overall Diameter | |||
| Circumference | |||
| Revolutions / Mile | |||
| Ride Height | Baseline |
Speedometer Difference
If your speedometer reads 60 mph with the new tire installed, your estimated actual speed would be:
How to Use the Tire Size Comparison Calculator
Enter your current tire size in the first section and the tire size you are considering in the second section. Select the tire width, aspect ratio, and wheel diameter exactly as they appear in the tire size.
For example, a tire marked 225/60R17 has a nominal section width of 225 mm, an aspect ratio of 60%, and is designed for a 17-inch wheel.
After selecting both sizes, choose Compare Tire Sizes to see the dimensional differences and estimated speedometer change.
What the Tire Size Comparison Shows
The calculator compares several measurements that can change when moving from one tire size to another.
- Width: the nominal section width of the tire in millimeters.
- Sidewall height: the calculated height of one tire sidewall.
- Overall diameter: the approximate outside diameter of the mounted tire.
- Circumference: the approximate distance traveled during one complete tire revolution.
- Revolutions per mile: the estimated number of tire rotations required to travel one mile.
- Ride height change: approximately half of the overall diameter difference.
- Speedometer difference: an estimate of how a diameter change may affect indicated vehicle speed.
How Tire Diameter Is Calculated
Metric tire sizes provide the information needed to estimate overall tire diameter. Sidewall height is calculated by multiplying the tire width by its aspect ratio. The two sidewalls are then added to the wheel diameter.
For a 225/60R17 tire, the sidewall height is approximately 135 mm. The calculator converts the 17-inch wheel diameter into millimeters and adds two sidewalls to estimate the complete tire diameter.
Why Overall Diameter Matters
Changing overall tire diameter can affect more than appearance. A larger or smaller rolling diameter may change speedometer readings, effective gearing, ride height, wheel-well clearance, and the number of tire revolutions per mile.
A commonly referenced comparison guideline is to keep replacement tire diameter relatively close to the original size, often within approximately 3%. However, the percentage alone does not determine whether a tire is appropriate for a particular vehicle.
Understanding Speedometer Difference
A vehicle's speedometer is calibrated around the expected rolling circumference of its original tire setup. Changing tire diameter changes the distance traveled during each wheel revolution.
If the replacement tire is larger in diameter, the vehicle generally travels slightly farther per revolution than the original tire. If it is smaller, it travels a shorter distance per revolution. The calculator estimates this difference using the calculated tire diameters.
Does a Similar Diameter Mean the Tire Will Fit?
No. Similar overall diameter is only one part of tire and wheel fitment.
A replacement tire may have a similar diameter but still be substantially wider. Actual fitment can also depend on wheel width, wheel offset, backspacing, suspension clearance, brake clearance, fender clearance, load requirements, and the exact vehicle configuration.
Always verify important fitment specifications before purchasing or installing a different tire size.
Tire Size Comparison FAQ
What does 225/60R17 mean?
225 is the nominal tire width in millimeters. 60 is the aspect ratio, meaning the sidewall height is approximately 60% of the tire width. R indicates radial construction, and 17 is the wheel diameter in inches.
How much tire size difference is acceptable?
A difference of roughly 3% or less in overall diameter is commonly used as an initial comparison guideline. It is not a universal fitment rule. Vehicle manufacturers may specify different requirements, and clearance, load rating, wheel dimensions, and other factors must also be considered.
Will changing tire size affect my speedometer?
It can. Increasing overall tire diameter generally causes the vehicle to travel slightly faster than the speedometer indicates, while decreasing diameter can have the opposite effect.
Can two different tire sizes have nearly the same diameter?
Yes. Different combinations of tire width, aspect ratio, and wheel diameter can produce similar overall diameters. This is common when comparing alternative or plus-size tire configurations.
Does this calculator guarantee tire fitment?
No. The calculator compares mathematical tire dimensions. It does not account for every vehicle-specific factor such as wheel offset, suspension geometry, brake clearance, fender clearance, or modifications.
Before Changing Tire Size
Use this calculator as a comparison tool rather than a final fitment approval. Before purchasing tires, verify the correct size, load rating, speed rating, wheel compatibility, inflation requirements, and vehicle clearance using manufacturer specifications or a qualified tire professional.