275/50R21
275/50R21 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 31.83″ diameter with a 5.41″ sidewall (50% of section width), this size turns 634 revolutions per mile.
About 275/50R21
275/50R21 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 31.83″ overall diameter, 275/50R21 turns 634 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 295/45R21 drops diameter by 1.18%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 285/50R21 adds 1.24% 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 31.83″ 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 aliases275/50R21
- Diameter
- 31.83″ / 808.4mm
- Section Width
- 10.83″
- Sidewall
- 5.41″ / 137.5mm
- Circumference
- 99.99″
- Revs/Mile
- 634
265/45R21
- Diameter
- 30.39″ / 771.9mm
- Section Width
- 10.43″
- Sidewall
- 4.69″ / 119.25mm
- Circumference
- 95.47″
- Revs/Mile
- 664
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 57.29 mph (92.2 km/h). Your speedometer reads 4.52% high versus actual speed.