Tire Size Calculator
Compare different tire sizes and see how they affect your vehicle
Fitment and safety notice: This calculator is an estimate, not a vehicle fitment approval. Before changing tire or wheel size, confirm clearance, load index, speed rating, wheel specifications, vehicle calibration, and applicable local requirements for your exact year, make, model, trim, and modifications. Consult manufacturer information or a qualified technician for safety-critical decisions.
Original Tire
New Tire
Enter Your Current Tire Size
Plus Size Options
Select an option to compare with your current tire size:
Comparison with Selected Size
225/45R17
245/40R18
24.7″
25.7″
| Dimension | Original | Plus Size | Difference |
|---|---|---|---|
| Tire Size | 225/45R17 | 245/40R18 | – |
| Diameter | 24.7″ | 25.7″ | +1.0″ (+4.0%) |
| Width | 8.9″ | 9.6″ | +0.7″ (+8.9%) |
| Circumference | 77.6″ | 80.7″ | +3.1″ (+4.0%) |
| Speedometer Error | 0% | -4.0% | At 60 mph: 62.4 mph actual |
Plus Sizing Notes
- Plus sizing maintains a similar overall diameter while increasing rim size and decreasing sidewall height.
- The selected plus size tire is within 2% of your original tire’s diameter.
- A wider tire may require a wider wheel. Check manufacturer recommendations.
- Lower profile tires (smaller aspect ratio) generally provide better handling but may offer a firmer ride.
225/45R17
245/40R18
24.7″
25.7″
Results
| Dimension | Original | New | Difference |
|---|---|---|---|
| Tire Size | 225/45R17 | 245/40R18 | – |
| Diameter | 24.7″ | 25.7″ | +1.0″ (+4.0%) |
| Width | 8.9″ | 9.6″ | +0.7″ (+8.9%) |
| Circumference | 77.6″ | 80.7″ | +3.1″ (+4.0%) |
| Sidewall Height | 4.0″ | 3.8″ | -0.2″ (-5.0%) |
| Revolutions/Mile | 815 | 785 | -30 (-3.7%) |
| Effect | Value | Description |
|---|---|---|
| Speedometer | -4.0% | Your speedometer will read slower than actual speed |
| At 60 mph | 62.4 mph | Actual speed when speedometer shows 60 mph |
| Ground Clearance | +0.5″ | Change in distance from ground to chassis |
| Wheel Well Clearance | -0.2″ | Change in space between tire and wheel well |
| Wheel Poke | +5mm | How much the wheel sticks out from the fender |
Fitment Notes
- The new tire is 4.0% larger in diameter, which may affect speedometer accuracy.
- The new tire is 8.9% wider, which may affect clearance in the wheel well.
- The new wheel has a 5mm different offset, which will change the wheel position relative to the fender.
- Always ensure proper clearance between the tire and suspension components, fenders, and wheel wells.