255/45R21
255/45R21 ships as an OEM size on the Lincoln Nautilus, Volkswagen Atlas. At 30.04″ diameter with a 4.52″ sidewall (45% of section width), this size turns 671 revolutions per mile.
About 255/45R21
Factory fitments for 255/45R21 include the Lincoln Nautilus, Volkswagen Atlas — meaning replacement tires in this size see steady demand and broad brand availability. At 30.04″ overall diameter, 255/45R21 turns 671 revolutions per mile, which is the reference point the factory speedometer and odometer were calibrated against. The 45% aspect ratio gives it a low-profile sidewall that delivers sharp steering response but transmits road imperfections. The 21″ rim pairing is typical for luxury SUV and performance-oriented platforms, so compatible wheels are easy to source new or used. Going one step shorter to 275/40R21 drops diameter by 1.25%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 235/50R21 adds 0.72% 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 30.04″ 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 aliases255/45R21
- Diameter
- 30.04″ / 762.9mm
- Section Width
- 10.04″
- Sidewall
- 4.52″ / 114.75mm
- Circumference
- 94.36″
- Revs/Mile
- 671
235/50R21
- Diameter
- 30.25″ / 768.4mm
- Section Width
- 9.25″
- Sidewall
- 4.63″ / 117.5mm
- Circumference
- 95.04″
- Revs/Mile
- 667
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 60.43 mph (97.26 km/h). Your speedometer reads 0.72% low versus actual speed.