255/50R18
255/50R18 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 28.04″ diameter with a 5.02″ sidewall (50% of section width), this size turns 719 revolutions per mile.
About 255/50R18
255/50R18 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 28.04″ overall diameter, 255/50R18 turns 719 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 245/50R18 drops diameter by 1.40%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 235/55R18 adds 0.49% 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 28.04″ 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 aliases255/50R18
- Diameter
- 28.04″ / 712.2mm
- Section Width
- 10.04″
- Sidewall
- 5.02″ / 127.5mm
- Circumference
- 88.09″
- Revs/Mile
- 719
235/50R18
- Diameter
- 27.25″ / 692.2mm
- Section Width
- 9.25″
- Sidewall
- 4.63″ / 117.5mm
- Circumference
- 85.61″
- Revs/Mile
- 740
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.32 mph (93.85 km/h). Your speedometer reads 2.81% high versus actual speed.