305/55R20
305/55R20 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 33.21″ diameter with a 6.60″ sidewall (55% of section width), this size turns 607 revolutions per mile.
About 305/55R20
305/55R20 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 33.21″ overall diameter, 305/55R20 turns 607 revolutions per mile, which is the reference point the factory speedometer and odometer were calibrated against. The 55% aspect ratio gives it a moderate sidewall suited to sporty street driving and responsive turn-in. The 20″ 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 295/55R20 drops diameter by 1.30%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 285/60R20 adds 0.77% 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 33.21″ 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 aliases305/55R20
- Diameter
- 33.21″ / 843.5mm
- Section Width
- 12.01″
- Sidewall
- 6.6″ / 167.75mm
- Circumference
- 104.33″
- Revs/Mile
- 607
285/55R20
- Diameter
- 32.34″ / 821.5mm
- Section Width
- 11.22″
- Sidewall
- 6.17″ / 156.75mm
- Circumference
- 101.61″
- Revs/Mile
- 624
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.44 mph (94.04 km/h). Your speedometer reads 2.61% high versus actual speed.