255/40R19 vs 245/45R19
245/45R19 has an overall diameter of 703.1 mm (27.68") compared with 686.6 mm (27.03") for 255/40R19, a difference of +16.5 mm (+2.40 %). The sidewall changes by +8.3 mm, section width by -10 mm and ride height by +8.3 mm. Using the ETRTO rolling circumference, 255/40R19 turns 478 times per kilometre and 245/45R19 turns 466 times. With 245/45R19 fitted to a car calibrated for 255/40R19, an indicated 100 km/h is a true 102.4 km/h, and the odometer records 97.7 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 255/40R19 | 245/45R19 | Difference |
|---|---|---|---|
| Section width | 255 mm | 245 mm | -10 mm |
| Sidewall height | 102.0 mm | 110.3 mm | +8.3 mm |
| Rim diameter | 19" | 19" | 0.0" |
| Overall diameter | 686.6 mm (27.03") | 703.1 mm (27.68") | +16.5 mm (+2.40 %) |
| Static circumference | 2157 mm | 2209 mm | +52 mm |
| Rolling circumference (ETRTO) | 2094 mm | 2144 mm | +50 mm |
| Revs per km | 478 | 466 | -11 |
| Ride height | +8.3 mm | ||
| Inch equivalent | 27x10R19 | 27.7×9.6R19 | |
| Approved rim widths (approx.) | 8.5″–10″ | 7.5″–9″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 41.0 | 51.2 | 61.4 | 81.9 | 102.4 | 112.6 |
| Error (km/h) | +1.0 | +1.2 | +1.4 | +1.9 | +2.4 | +2.6 |
Assumes the speedo was accurate on 255/40R19. Odometer records 97.7 km for every 100 km actually driven.
- The 245/45R19 is 16.5 mm (2.4 %) larger in diameter, so your speedo will read low and your odometer will under-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 245/45R19 legal in Australia? Needs certification
| Overall diameter (VSB 14 LS 4.2.4) 245/45R19 is 16.5 mm larger than 255/40R19; the limit without certification for a passenger car (MA/MB) is +15 mm. Larger increases need an approved signatory / engineering certificate (modification code LS or state equivalent) and may not be permitted at all. | Cert. |
| Speedometer (ADR 18/03) A larger tyre makes the speedo read lower: at an indicated 100 km/h you would be doing 102.4 km/h. ADR 18 requires the speedo never to read below true speed, but factory speedos typically over-read by 2-6 %, so a 2.4 % increase is usually absorbed. Verify with a GPS speed app after fitting. | Verify |
| 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 245/45R19 instead of 255/40R19?
Overall diameter changes by +16.5 mm (+2.40 %). 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 245/45R19?
Your speedo will read low by about 2.40 %. At an indicated 100 km/h you would actually be travelling 102.4 km/h, and at 110 km/h about 112.6 km/h.
What is the rolling circumference of 245/45R19?
Static circumference is 2209 mm; the ETRTO rolling circumference under load is about 2144 mm, which is 466 revolutions per kilometre.
245/45R19 in inches
245/45R19 is approximately 27.7×9.6R19: 27.7" tall, 9.6" wide, on a 19" rim, with a 4.3" sidewall.
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