235/40R18
235/40R18 ships as an OEM size on the Acura Integra, Honda Civic. At 25.40″ diameter with a 3.70″ sidewall (40% of section width), this size turns 794 revolutions per mile.
About 235/40R18
Factory fitments for 235/40R18 include the Acura Integra, Honda Civic — meaning replacement tires in this size see steady demand and broad brand availability. At 25.40″ overall diameter, 235/40R18 turns 794 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 225/40R18 drops diameter by 1.24%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 215/45R18 adds 0.85% 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 25.40″ 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 aliases235/40R18
- Diameter
- 25.4″ / 645.2mm
- Section Width
- 9.25″
- Sidewall
- 3.7″ / 94mm
- Circumference
- 79.8″
- Revs/Mile
- 794
215/40R18
- Diameter
- 24.77″ / 629.2mm
- Section Width
- 8.46″
- Sidewall
- 3.39″ / 86mm
- Circumference
- 77.82″
- Revs/Mile
- 814
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.51 mph (94.17 km/h). Your speedometer reads 2.48% high versus actual speed.