245/40R18 vs 245/45R18 Side-by-side tire size comparison with specs and compatibility
Compatibility
+3.75% diameter difference
⚠ Swap with Caution
This tire swap is between 3-5% diameter difference. Check for fender clearance and be aware of speedometer error. May require recalibration.
Full Specifications Comparison
| Specification | 245/40R18 | 245/45R18 | Difference |
|---|---|---|---|
| Overall Diameter | 653.2 mm (25.7") | 677.7 mm (26.7") | +24.5 mm |
| Section Width | 245 mm (9.6") | 245 mm (9.6") | 0 mm |
| Sidewall Height | 98 mm | 110.3 mm | +12.3 mm |
| Circumference | 2052.1 mm | 2129.1 mm | +77 mm |
| Revolutions/Mile | 784 | 756 | -28 |
| Aspect Ratio | 40% | 45% | +5% |
| Rim Diameter | 18" | 18" | 0" |
Key Impact Summary
Ground Clearance
+12.3 mm
Speedometer Error
+3.75%
Width Change
0 mm
Sidewall Change
+12.3 mm
Speedometer Correction Table
When switching from 245/40R18 to 245/45R18, your speedometer will under-read. Here is the correction at common speeds:
| Speedometer Shows | Actual Speed (mph) | Difference |
|---|---|---|
| 30 mph | 31.1 mph | +1.1 mph |
| 40 mph | 41.5 mph | +1.5 mph |
| 50 mph | 51.9 mph | +1.9 mph |
| 60 mph | 62.3 mph | +2.3 mph |
| 70 mph | 72.6 mph | +2.6 mph |
| 80 mph | 83 mph | +3 mph |
| 90 mph | 93.4 mph | +3.4 mph |
| 100 mph | 103.8 mph | +3.8 mph |
| 110 mph | 114.1 mph | +4.1 mph |
| 120 mph | 124.5 mph | +4.5 mph |
What This Swap Means
Taller sidewall: The 12.3mm increase in sidewall height provides a more comfortable ride by absorbing more road imperfections. Taller sidewalls also offer better protection against pothole damage to wheels. The trade-off is slightly less responsive steering feel.
Ground clearance: Increases by 12.3mm, providing slightly better approach angles for off-road driving and speed bump clearance.
Vehicles Using 245/40R18
2025 Audi A4 Premium 40 TFSI 2025 Audi A4 Premium Plus 45 TFSI quattro 2024 Audi A4 Premium Plus 45 TFSI quattro 2023 Audi A4 Premium Plus 45 TFSI quattro 2022 Audi A4 Premium Plus 45 TFSI quattro 2021 Audi A4 Premium Plus 45 TFSI quattro 2020 Audi A4 Premium Plus 45 TFSI quattro 2025 Mercedes-Benz C-Class C 300 2025 Mercedes-Benz C-Class C 300 4MATIC 2024 Mercedes-Benz C-Class C 300
Vehicles Using 245/45R18
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Individual Tire Specs
Frequently Asked Questions
This swap requires caution. The diameter difference is +3.75% (+24.5mm). This exceeds the recommended 3% threshold and may affect speedometer accuracy, ABS calibration, and could cause clearance issues.
Switching from 245/40R18 to 245/45R18 creates a +3.75% speedometer error. Your actual speed will be faster than displayed — at an indicated 60 mph, you'll actually be going 62.3 mph.
Switching from 245/40R18 to 245/45R18 changes ground clearance by +12.3mm. The vehicle will sit 12.3mm higher. Ground clearance change equals half the overall diameter difference.