275/40R18
275/40R18 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 26.66″ diameter with a 4.33″ sidewall (40% of section width), this size turns 756 revolutions per mile.
About 275/40R18
275/40R18 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 26.66″ overall diameter, 275/40R18 turns 756 revolutions per mile, which is the reference point the factory speedometer and odometer were calibrated against. The 40% aspect ratio gives it a low-profile sidewall that delivers sharp steering response but transmits road imperfections. The 18″ rim pairing is typical for full-size truck, premium SUV, and sport-sedan platforms, so compatible wheels are easy to source new or used. Going one step shorter to 265/40R18 drops diameter by 1.18%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 285/40R18 adds 1.18% diameter — also inside the safe window, with marginally taller ride height. If you are shopping for a direct replacement, any tire within roughly ±0.7″ of the 26.66″ stock diameter (about ±2% in percentage terms) will keep ABS, TPMS, and odometer readings inside the vehicle's designed tolerance.
Compare with another size
275/65R18 or "33" for inch aliases275/40R18
- Diameter
- 26.66″ / 677.2mm
- Section Width
- 10.83″
- Sidewall
- 4.33″ / 110mm
- Circumference
- 83.76″
- Revs/Mile
- 756
255/40R18
- Diameter
- 26.03″ / 661.2mm
- Section Width
- 10.04″
- Sidewall
- 4.02″ / 102mm
- Circumference
- 81.78″
- Revs/Mile
- 775
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.58 mph (94.28 km/h). Your speedometer reads 2.36% high versus actual speed.