285/50R18
285/50R18 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 29.22″ diameter with a 5.61″ sidewall (50% of section width), this size turns 690 revolutions per mile.
About 285/50R18
285/50R18 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 29.22″ overall diameter, 285/50R18 turns 690 revolutions per mile, which is the reference point the factory speedometer and odometer were calibrated against. The 50% 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 275/50R18 drops diameter by 1.35%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 265/55R18 adds 0.88% 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 29.22″ 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 aliases285/50R18
- Diameter
- 29.22″ / 742.2mm
- Section Width
- 11.22″
- Sidewall
- 5.61″ / 142.5mm
- Circumference
- 91.8″
- Revs/Mile
- 690
265/50R18
- Diameter
- 28.43″ / 722.2mm
- Section Width
- 10.43″
- Sidewall
- 5.22″ / 132.5mm
- Circumference
- 89.33″
- Revs/Mile
- 709
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.38 mph (93.96 km/h). Your speedometer reads 2.69% high versus actual speed.