285/50R21
285/50R21 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 32.22″ diameter with a 5.61″ sidewall (50% of section width), this size turns 626 revolutions per mile.
About 285/50R21
285/50R21 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 32.22″ overall diameter, 285/50R21 turns 626 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 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 275/50R21 drops diameter by 1.22%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 295/50R21 adds 1.22% 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 32.22″ 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 aliases285/50R21
- Diameter
- 32.22″ / 818.4mm
- Section Width
- 11.22″
- Sidewall
- 5.61″ / 142.5mm
- Circumference
- 101.22″
- Revs/Mile
- 626
265/50R21
- Diameter
- 31.43″ / 798.4mm
- Section Width
- 10.43″
- Sidewall
- 5.22″ / 132.5mm
- Circumference
- 98.75″
- Revs/Mile
- 642
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.53 mph (94.2 km/h). Your speedometer reads 2.44% high versus actual speed.