245/40R18 vs 245/45R18Tire Size Comparison

Use Caution

The 3.8% diameter difference exceeds 3% and may affect speedometer accuracy.

245/40R18653mm dia245/45R18678mm dia+12.3mm

Comparison Details

Overall Diameter653.2 vs 677.7 mm (+24.5 mm)
Diameter Difference+3.75%
Section Width245 vs 245 mm (0 mm)
Sidewall Height98.0 vs 110.3 mm (+12.3 mm)
Circumference2052.1 vs 2129.1 mm
Clearance Change+12.3 mm
Speedometer Error+3.75%
Revs/Mile784 vs 756

Speedometer Correction

When switching from 245/40R18 to 245/45R18, your speedometer will differ from actual speed.

SpeedometerActual SpeedDifference
30 km/h31.1 km/h+1.1 km/h
40 km/h41.5 km/h+1.5 km/h
50 km/h51.9 km/h+1.9 km/h
60 km/h62.3 km/h+2.3 km/h
70 km/h72.6 km/h+2.6 km/h
80 km/h83.0 km/h+3.0 km/h
90 km/h93.4 km/h+3.4 km/h
100 km/h103.8 km/h+3.8 km/h
110 km/h114.1 km/h+4.1 km/h
120 km/h124.5 km/h+4.5 km/h
130 km/h134.9 km/h+4.9 km/h

Vehicles Using These Sizes

Vehicles with 245/40R18

2025 Audi A4Premium 40 TFSI2025 Audi A4Premium Plus 45 TFSI quattro2024 Audi A4Premium Plus 45 TFSI quattro2023 Audi A4Premium Plus 45 TFSI quattro2022 Audi A4Premium Plus 45 TFSI quattro2021 Audi A4Premium Plus 45 TFSI quattro2020 Audi A4Premium Plus 45 TFSI quattro2025 Mercedes-Benz C-ClassC 3002025 Mercedes-Benz C-ClassC 300 4MATIC2024 Mercedes-Benz C-ClassC 3002024 Mercedes-Benz C-ClassC 300 4MATIC2023 Mercedes-Benz C-ClassC 3002023 Mercedes-Benz C-ClassC 300 4MATIC

Vehicles with 245/45R18

2025 Dodge ChargerSixpack2025 Infiniti Q50Luxe2024 Infiniti Q50Luxe

Individual Tire Size Details

245/40R18
Full specifications, compatible vehicles, and alternatives
245/45R18
Full specifications, compatible vehicles, and alternatives

Practical Guidance

The 3.8% diameter difference between 245/40R18 and 245/45R18 exceeds the standard 3% tolerance. While physically possible, this change will cause noticeable speedometer error and may affect ABS and traction control calibration. Consult a tire professional before making this switch.

The 3% diameter tolerance is a widely accepted industry guideline referenced by the ETRTO and most vehicle manufacturers. When in doubt, consult your vehicle's owner's manual or a qualified tire professional. For U.S. tire safety standards and recalls, see the NHTSA Tire Safety page.

Frequently Asked Questions

Use Caution. The overall diameter differs by 3.75%, width changes by 0mm.

Speedometer error will be 3.75%. At an indicated 100 km/h, actual speed is about 103.8 km/h.

Ground clearance changes by +12.3mm per side.