275/55R19 vs 255/60R18
255/60R18 has an overall diameter of 763.2 mm (30.05") compared with 785.1 mm (30.91") for 275/55R19, a difference of -21.9 mm (-2.79 %). The sidewall changes by +1.8 mm, section width by -20 mm and ride height by -10.9 mm. Using the ETRTO rolling circumference, 275/55R19 turns 418 times per kilometre and 255/60R18 turns 430 times. With 255/60R18 fitted to a car calibrated for 275/55R19, an indicated 100 km/h is a true 97.2 km/h, and the odometer records 102.9 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 275/55R19 | 255/60R18 | Difference |
|---|---|---|---|
| Section width | 275 mm | 255 mm | -20 mm |
| Sidewall height | 151.3 mm | 153.0 mm | +1.8 mm |
| Rim diameter | 19" | 18" | -1.0" |
| Overall diameter | 785.1 mm (30.91") | 763.2 mm (30.05") | -21.9 mm (-2.79 %) |
| Static circumference | 2466 mm | 2398 mm | -69 mm |
| Rolling circumference (ETRTO) | 2395 mm | 2328 mm | -67 mm |
| Revs per km | 418 | 430 | +12 |
| Ride height | -10.9 mm | ||
| Inch equivalent | 30.9×10.8R19 | 30x10R18 | |
| Approved rim widths (approx.) | 7.5″–9.5″ | 7″–8.5″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 38.9 | 48.6 | 58.3 | 77.8 | 97.2 | 106.9 |
| Error (km/h) | -1.1 | -1.4 | -1.7 | -2.2 | -2.8 | -3.1 |
Assumes the speedo was accurate on 275/55R19. Odometer records 102.9 km for every 100 km actually driven.
- The 255/60R18 is 21.9 mm (2.79 %) smaller in diameter, so your speedo will read high and your odometer will over-record distance.
- Section width changes by -20 mm. Check guard, strut and inner-arch clearance and that the rim width is within the approved range for the new tyre.
- Rim diameter changes from 19" to 18", so new wheels are required.
Is 255/60R18 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -21.9 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 97.2 km/h (over-read 2.8 km/h; ADR 18 allows up to 13.7 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 255/60R18 instead of 275/55R19?
Overall diameter changes by -21.9 mm (-2.79 %). 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 255/60R18?
Your speedo will read high by about 2.79 %. At an indicated 100 km/h you would actually be travelling 97.2 km/h, and at 110 km/h about 106.9 km/h.
What is the rolling circumference of 255/60R18?
Static circumference is 2398 mm; the ETRTO rolling circumference under load is about 2328 mm, which is 430 revolutions per kilometre.
255/60R18 in inches
255/60R18 is approximately 30x10R18: 30.0" tall, 10.0" wide, on a 18" rim, with a 6.0" sidewall.
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