255/40R19
255/40R19 ships as an OEM size on the Ford Mustang. At 27.03″ diameter with a 4.02″ sidewall (40% of section width), this size turns 746 revolutions per mile.
About 255/40R19
Factory fitments for 255/40R19 include the Ford Mustang — meaning replacement tires in this size see steady demand and broad brand availability. At 27.03″ overall diameter, 255/40R19 turns 746 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 19″ rim pairing is typical for full-size truck, premium SUV, and sport-sedan platforms, so compatible wheels are easy to source new or used. Going one step shorter to 245/40R19 drops diameter by 1.17%, which stays within the ±3% fitment safe zone for most vehicles. Stepping up to 235/45R19 adds 1.09% 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 27.03″ 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 aliases255/40R19
- Diameter
- 27.03″ / 686.6mm
- Section Width
- 10.04″
- Sidewall
- 4.02″ / 102mm
- Circumference
- 84.92″
- Revs/Mile
- 746
235/40R19
- Diameter
- 26.4″ / 670.6mm
- Section Width
- 9.25″
- Sidewall
- 3.7″ / 94mm
- Circumference
- 82.94″
- Revs/Mile
- 764
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 58.6 mph (94.31 km/h). Your speedometer reads 2.33% high versus actual speed.