305/55R18
305/55R18 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 31.21″ diameter with a 6.60″ sidewall (55% of section width), this size turns 646 revolutions per mile.
About 305/55R18
305/55R18 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 31.21″ overall diameter, 305/55R18 turns 646 revolutions per mile, which is the reference point the factory speedometer and odometer were calibrated against. The 55% aspect ratio gives it a moderate sidewall suited to sporty street driving and responsive turn-in. 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 295/55R18 drops diameter by 1.39%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 285/60R18 adds 0.82% 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 31.21″ 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 aliases305/55R18
- Diameter
- 31.21″ / 792.7mm
- Section Width
- 12.01″
- Sidewall
- 6.6″ / 167.75mm
- Circumference
- 98.04″
- Revs/Mile
- 646
285/55R18
- Diameter
- 30.34″ / 770.7mm
- Section Width
- 11.22″
- Sidewall
- 6.17″ / 156.75mm
- Circumference
- 95.32″
- Revs/Mile
- 665
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.33 mph (93.88 km/h). Your speedometer reads 2.78% high versus actual speed.