245/40R18 Tire Size Specifications & Compatible Vehicles

Overall Diameter

653.2 mm

Section Width

245 mm

Sidewall Height

98.0 mm

Circumference

2052.1 mm

Revs/Mile

784

Rim Diameter

18"

Inch Equivalent

25.7x9.6R18

Rim Width (ETRTO)

7.0" – 9.0"

Compatible Vehicles

The following vehicles use 245/40R18 tires from the factory:

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 2024 Mercedes-Benz C-Class C 300 4MATIC 2023 Mercedes-Benz C-Class C 300 2023 Mercedes-Benz C-Class C 300 4MATIC

Alternative Tire Sizes

These tire sizes are within 3% overall diameter of 245/40R18 and may be used as replacements:

155/55R19 Safe 0.0% diff 285/30R19 Safe 0.1% diff 185/60R17 Safe 0.1% diff 165/75R16 Safe 0.1% diff 225/55R16 Safe 0.1% diff 275/45R16 Safe 0.1% diff 205/60R16 Safe 0.1% diff 245/45R17 Safe 0.1% diff 315/35R17 Safe 0.1% diff 245/35R19 Safe 0.1% diff 195/50R18 Safe 0.1% diff 325/30R18 Safe 0.1% diff

Popular Comparisons

See how 245/40R18 compares to other common tire sizes:

225/45R17 vs 245/40R18 Performance upgrade wider + bigger rim 235/45R18 vs 245/40R18 Wider, lower-profile swap 245/40R18 vs 255/40R19 Performance car upgrade path 225/40R18 vs 245/40R18 Width upgrade on 18-inch 245/40R18 vs 245/45R18 Profile height comparison

Understanding 245/40R18

The tire size 245/40R18 means the tire has a section width of 245mm, an aspect ratio of 40% (the sidewall height is 40% of the width), and fits a 18-inch rim.

Sidewall Height = 245 x 0.4 = 98.0 mm
Overall Diameter = (98.0 x 2) + (18 x 25.4) = 653.2 mm
Circumference = 653.2 x π = 2052.1 mm

Frequently Asked Questions

What vehicles use 245/40R18 tires? ▼

The 245/40R18 tire size is used on 13 vehicle trims including the 2025 Audi A4, 2025 Audi A4, 2024 Audi A4 and 10 more.

What is the diameter of a 245/40R18 tire? ▼

A 245/40R18 tire has an overall diameter of 653.2mm (25.7 inches). The sidewall height is 98.0mm, and the total circumference is 2052mm.

What rim width do I need for 245/40R18 tires? ▼

For 245/40R18 tires, the ETRTO recommended rim width is 8.0". The acceptable range is 7.0" minimum to 9.0" maximum. Using a rim outside this range can cause improper bead seating and unsafe handling.

Can I replace 245/40R18 with a different size? ▼

Yes, as long as the replacement tire overall diameter is within 3% of the 245/40R18 653.2mm diameter. Compatible alternatives include 155/55R19, 285/30R19, 185/60R17. Use our Tire Size Calculator to compare any two sizes.