265/65R17 vs 285/60R18
285/60R18 has an overall diameter of 799.2 mm (31.46") compared with 776.3 mm (30.56") for 265/65R17, a difference of +22.9 mm (+2.95 %). The sidewall changes by -1.2 mm, section width by +20 mm and ride height by +11.5 mm. Using the ETRTO rolling circumference, 265/65R17 turns 422 times per kilometre and 285/60R18 turns 410 times. With 285/60R18 fitted to a car calibrated for 265/65R17, an indicated 100 km/h is a true 102.9 km/h, and the odometer records 97.1 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 265/65R17 | 285/60R18 | Difference |
|---|---|---|---|
| Section width | 265 mm | 285 mm | +20 mm |
| Sidewall height | 172.3 mm | 171.0 mm | -1.2 mm |
| Rim diameter | 17" | 18" | +1.0" |
| Overall diameter | 776.3 mm (30.56") | 799.2 mm (31.46") | +22.9 mm (+2.95 %) |
| Static circumference | 2439 mm | 2511 mm | +72 mm |
| Rolling circumference (ETRTO) | 2368 mm | 2438 mm | +70 mm |
| Revs per km | 422 | 410 | -12 |
| Ride height | +11.5 mm | ||
| Inch equivalent | 30.6×10.4R17 | 31.5×11.2R18 | |
| Approved rim widths (approx.) | 7.5″–9″ | 8″–9.5″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 41.2 | 51.5 | 61.8 | 82.4 | 102.9 | 113.2 |
| Error (km/h) | +1.2 | +1.5 | +1.8 | +2.4 | +2.9 | +3.2 |
Assumes the speedo was accurate on 265/65R17. Odometer records 97.1 km for every 100 km actually driven.
- The 285/60R18 is 22.9 mm (2.95 %) larger in diameter, so your speedo will read low and your odometer will under-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 17" to 18", so new wheels are required.
Is 285/60R18 legal in Australia? Needs certification
| Overall diameter (VSB 14 LS 4.2.4) 285/60R18 is 22.9 mm larger than 265/65R17; 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 102.9 km/h. ADR 18 requires the speedo never to read below true speed, but factory speedos typically over-read by 2-6 %, so a 2.9 % 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 285/60R18 instead of 265/65R17?
Overall diameter changes by +22.9 mm (+2.95 %). 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 285/60R18?
Your speedo will read low by about 2.95 %. At an indicated 100 km/h you would actually be travelling 102.9 km/h, and at 110 km/h about 113.2 km/h.
What is the rolling circumference of 285/60R18?
Static circumference is 2511 mm; the ETRTO rolling circumference under load is about 2438 mm, which is 410 revolutions per kilometre.
285/60R18 in inches
285/60R18 is approximately 31.5×11.2R18: 31.5" tall, 11.2" wide, on a 18" rim, with a 6.7" sidewall.
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