255/60R18 vs 235/55R19
235/55R19 has an overall diameter of 741.1 mm (29.18") compared with 763.2 mm (30.05") for 255/60R18, a difference of -22.1 mm (-2.90 %). The sidewall changes by -23.7 mm, section width by -20 mm and ride height by -11.1 mm. Using the ETRTO rolling circumference, 255/60R18 turns 430 times per kilometre and 235/55R19 turns 442 times. With 235/55R19 fitted to a car calibrated for 255/60R18, an indicated 100 km/h is a true 97.1 km/h, and the odometer records 103 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 255/60R18 | 235/55R19 | Difference |
|---|---|---|---|
| Section width | 255 mm | 235 mm | -20 mm |
| Sidewall height | 153.0 mm | 129.3 mm | -23.7 mm |
| Rim diameter | 18" | 19" | +1.0" |
| Overall diameter | 763.2 mm (30.05") | 741.1 mm (29.18") | -22.1 mm (-2.90 %) |
| Static circumference | 2398 mm | 2328 mm | -69 mm |
| Rolling circumference (ETRTO) | 2328 mm | 2260 mm | -67 mm |
| Revs per km | 430 | 442 | +13 |
| Ride height | -11.1 mm | ||
| Inch equivalent | 30x10R18 | 29.2×9.3R19 | |
| Approved rim widths (approx.) | 7″–8.5″ | 6.5″–8.5″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 38.8 | 48.6 | 58.3 | 77.7 | 97.1 | 106.8 |
| Error (km/h) | -1.2 | -1.4 | -1.7 | -2.3 | -2.9 | -3.2 |
Assumes the speedo was accurate on 255/60R18. Odometer records 103.0 km for every 100 km actually driven.
- The 235/55R19 is 22.1 mm (2.9 %) 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 18" to 19", so new wheels are required.
Is 235/55R19 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -22.1 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 97.1 km/h (over-read 2.9 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 235/55R19 instead of 255/60R18?
Overall diameter changes by -22.1 mm (-2.90 %). 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 235/55R19?
Your speedo will read high by about 2.90 %. At an indicated 100 km/h you would actually be travelling 97.1 km/h, and at 110 km/h about 106.8 km/h.
What is the rolling circumference of 235/55R19?
Static circumference is 2328 mm; the ETRTO rolling circumference under load is about 2260 mm, which is 442 revolutions per kilometre.
235/55R19 in inches
235/55R19 is approximately 29.2×9.3R19: 29.2" tall, 9.3" wide, on a 19" rim, with a 5.1" sidewall.
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