305/50R18
305/50R18 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 30.01″ diameter with a 6.00″ sidewall (50% of section width), this size turns 672 revolutions per mile.
About 305/50R18
305/50R18 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 30.01″ overall diameter, 305/50R18 turns 672 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 295/50R18 drops diameter by 1.31%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 285/55R18 adds 1.12% 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 30.01″ 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 aliases305/50R18
- Diameter
- 30.01″ / 762.2mm
- Section Width
- 12.01″
- Sidewall
- 6″ / 152.5mm
- Circumference
- 94.27″
- Revs/Mile
- 672
285/50R18
- Diameter
- 29.22″ / 742.2mm
- Section Width
- 11.22″
- Sidewall
- 5.61″ / 142.5mm
- Circumference
- 91.8″
- Revs/Mile
- 690
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.43 mph (94.03 km/h). Your speedometer reads 2.62% high versus actual speed.