285/75R16 vs 275/65R18
275/65R18 has an overall diameter of 814.7 mm (32.07") compared with 833.9 mm (32.83") for 285/75R16, a difference of -19.2 mm (-2.30 %). The sidewall changes by -35.0 mm, section width by -10 mm and ride height by -9.6 mm. Using the ETRTO rolling circumference, 285/75R16 turns 393 times per kilometre and 275/65R18 turns 402 times. With 275/65R18 fitted to a car calibrated for 285/75R16, 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 | 285/75R16 | 275/65R18 | Difference |
|---|---|---|---|
| Section width | 285 mm | 275 mm | -10 mm |
| Sidewall height | 213.8 mm | 178.8 mm | -35.0 mm |
| Rim diameter | 16" | 18" | +2.0" |
| Overall diameter | 833.9 mm (32.83") | 814.7 mm (32.07") | -19.2 mm (-2.30 %) |
| Static circumference | 2620 mm | 2559 mm | -60 mm |
| Rolling circumference (ETRTO) | 2543 mm | 2485 mm | -59 mm |
| Revs per km | 393 | 402 | +9 |
| Ride height | -9.6 mm | ||
| Inch equivalent | 32.8×11.2R16 | 32.1×10.8R18 | |
| Approved rim widths (approx.) | 7.5″–9″ | 7.5″–9″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 39.1 | 48.8 | 58.6 | 78.2 | 97.7 | 107.5 |
| Error (km/h) | -0.9 | -1.2 | -1.4 | -1.8 | -2.3 | -2.5 |
Assumes the speedo was accurate on 285/75R16. Odometer records 102.4 km for every 100 km actually driven.
- The 275/65R18 is 19.2 mm (2.3 %) 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.
- Rim diameter changes from 16" to 18", so new wheels are required.
Is 275/65R18 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -19.2 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 275/65R18 instead of 285/75R16?
Overall diameter changes by -19.2 mm (-2.30 %). 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 275/65R18?
Your speedo will read high by about 2.30 %. At an indicated 100 km/h you would actually be travelling 97.7 km/h, and at 110 km/h about 107.5 km/h.
What is the rolling circumference of 275/65R18?
Static circumference is 2559 mm; the ETRTO rolling circumference under load is about 2485 mm, which is 402 revolutions per kilometre.
275/65R18 in inches
275/65R18 is approximately 32.1×10.8R18: 32.1" tall, 10.8" wide, on a 18" rim, with a 7.0" sidewall.
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