255/40R19 vs 245/45R19
245/45R19 is taller than 255/40R19 by 2.40% — a diameter difference of 0.65″.
What changes between 255/40R19 and 245/45R19
Switching from 255/40R19 to 245/45R19 changes overall diameter by +2.40%, a taller tire by 0.65 inches. This lands inside the ±3% fitment safe zone, so most vehicles will accept the swap without rubbing, speedometer recalibration, or ABS/TPMS complications. Section width moves by -0.39″ (255mm → 245mm), which affects contact patch and fender-well clearance. Sidewall height shifts by +0.32″: a taller sidewall softens ride quality and adds off-road bump protection, with some loss of steering crispness. Revs per mile moves by -17, which translates directly to speedometer error — at an indicated 65 mph, actual speed becomes 66.6 mph. Both sizes share the same 19″ rim, so no wheel change is required — this is a pure tire-only swap.
| Spec | 255/40R19 | 245/45R19 |
|---|---|---|
| Overall diameter | 27.03″ | 27.68″ |
| Section width | 10.04″ (255 mm) | 9.65″ (245 mm) |
| Sidewall height | 4.02″ (40%) | 4.34″ (45%) |
| Rim diameter | 19″ | 19″ |
| Circumference | 84.92″ | 86.96″ |
| Revs per mile | 746 | 729 |
Interactive comparison
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
245/45R19
- Diameter
- 27.68″ / 703.1mm
- Section Width
- 9.65″
- Sidewall
- 4.34″ / 110.25mm
- Circumference
- 86.96″
- Revs/Mile
- 729
Speedometer & Diameter Impact
At an indicated 60 mph, your actual speed is 61.44 mph (98.88 km/h). Your speedometer reads 2.40% low versus actual speed.