235/40R20
235/40R20 is uncommon as OEM fitment but appears as an aftermarket upsize option. At 27.40″ diameter with a 3.70″ sidewall (40% of section width), this size turns 736 revolutions per mile.
About 235/40R20
235/40R20 is less common as a factory fitment but is available as an aftermarket size, so SKU selection is narrower than mainstream OEM sizes. At 27.40″ overall diameter, 235/40R20 turns 736 revolutions per mile, which is the reference point the factory speedometer and odometer were calibrated against. The 40% aspect ratio gives it a low-profile sidewall that delivers sharp steering response but transmits road imperfections. 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 255/35R20 drops diameter by 1.36%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 245/40R20 adds 1.15% 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 27.40″ 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 aliases235/40R20
- Diameter
- 27.4″ / 696mm
- Section Width
- 9.25″
- Sidewall
- 3.7″ / 94mm
- Circumference
- 86.08″
- Revs/Mile
- 736
235/35R20
- Diameter
- 26.48″ / 672.5mm
- Section Width
- 9.25″
- Sidewall
- 3.24″ / 82.25mm
- Circumference
- 83.18″
- Revs/Mile
- 762
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 57.97 mph (93.3 km/h). Your speedometer reads 3.38% high versus actual speed.