245/45R19 vs 255/40R19
255/40R19 has an overall diameter of 686.6 mm (27.03") compared with 703.1 mm (27.68") for 245/45R19, a difference of -16.5 mm (-2.35 %). The sidewall changes by -8.2 mm, section width by +10 mm and ride height by -8.2 mm. Using the ETRTO rolling circumference, 245/45R19 turns 466 times per kilometre and 255/40R19 turns 478 times. With 255/40R19 fitted to a car calibrated for 245/45R19, an indicated 100 km/h is a true 97.7 km/h, and the odometer records 102.4 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 245/45R19 | 255/40R19 | Difference |
|---|---|---|---|
| Section width | 245 mm | 255 mm | +10 mm |
| Sidewall height | 110.3 mm | 102.0 mm | -8.2 mm |
| Rim diameter | 19" | 19" | 0.0" |
| Overall diameter | 703.1 mm (27.68") | 686.6 mm (27.03") | -16.5 mm (-2.35 %) |
| Static circumference | 2209 mm | 2157 mm | -52 mm |
| Rolling circumference (ETRTO) | 2144 mm | 2094 mm | -50 mm |
| Revs per km | 466 | 478 | +11 |
| Ride height | -8.2 mm | ||
| Inch equivalent | 27.7×9.6R19 | 27x10R19 | |
| Approved rim widths (approx.) | 7.5″–9″ | 8.5″–10″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 39.1 | 48.8 | 58.6 | 78.1 | 97.7 | 107.4 |
| Error (km/h) | -0.9 | -1.2 | -1.4 | -1.9 | -2.3 | -2.6 |
Assumes the speedo was accurate on 245/45R19. Odometer records 102.4 km for every 100 km actually driven.
- The 255/40R19 is 16.5 mm (2.35 %) smaller in diameter, so your speedo will read high and your odometer will over-record distance.
- Section width changes by +10 mm. Check guard, strut and inner-arch clearance and that the rim width is within the approved range for the new tyre.
Is 255/40R19 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -16.5 mm is within the +15 mm / -26 mm allowance for a passenger car (MA/MB) (measured against the largest size the manufacturer designates for the model). | OK |
| Speedometer (ADR 18/03) A smaller tyre makes the speedo read high: at an indicated 100 km/h you would be doing 97.7 km/h (over-read 2.3 km/h; ADR 18 allows up to 13.8 km/h at that speed). | OK |
| Load index (tyre placard / ADR 42) Enter the placard load index and the replacement tyre load index to check. | ? |
| Speed rating (tyre placard / ADR 42) Enter the placard speed rating and the replacement tyre speed rating to check. | ? |
Frequently asked
Can I fit 255/40R19 instead of 245/45R19?
Overall diameter changes by -16.5 mm (-2.35 %). That is close to the 3 % rule of thumb; it may fit, but check guard, strut and brake clearance and your local rules. In Australia VSB 14 allows up to +15 mm for passenger cars and +50 mm for 4WDs/goods vehicles without certification.
How much will my speedo be out with 255/40R19?
Your speedo will read high by about 2.35 %. At an indicated 100 km/h you would actually be travelling 97.7 km/h, and at 110 km/h about 107.4 km/h.
What is the rolling circumference of 255/40R19?
Static circumference is 2157 mm; the ETRTO rolling circumference under load is about 2094 mm, which is 478 revolutions per kilometre.
255/40R19 in inches
255/40R19 is approximately 27x10R19: 27.0" tall, 10.0" wide, on a 19" rim, with a 4.0" sidewall.
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