315/50R21
315/50R21 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 33.40″ diameter with a 6.20″ sidewall (50% of section width), this size turns 604 revolutions per mile.
About 315/50R21
315/50R21 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 33.40″ overall diameter, 315/50R21 turns 604 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 305/50R21 drops diameter by 1.18%, which stays within the ±3% fitment safe zone for most vehicles. If you are shopping for a direct replacement, any tire within roughly ±0.7″ of the 33.40″ 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 aliases315/50R21
- Diameter
- 33.4″ / 848.4mm
- Section Width
- 12.4″
- Sidewall
- 6.2″ / 157.5mm
- Circumference
- 104.93″
- Revs/Mile
- 604
295/50R21
- Diameter
- 32.61″ / 828.4mm
- Section Width
- 11.61″
- Sidewall
- 5.81″ / 147.5mm
- Circumference
- 102.46″
- Revs/Mile
- 618
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.59 mph (94.28 km/h). Your speedometer reads 2.36% high versus actual speed.