265/70R17 vs 265/65R18
265/65R18 has an overall diameter of 801.7 mm (31.56") compared with 802.8 mm (31.61") for 265/70R17, a difference of -1.1 mm (-0.14 %). The sidewall changes by -13.2 mm, section width by 0 mm and ride height by -0.5 mm. Using the ETRTO rolling circumference, 265/70R17 turns 408 times per kilometre and 265/65R18 turns 409 times. With 265/65R18 fitted to a car calibrated for 265/70R17, an indicated 100 km/h is a true 99.9 km/h, and the odometer records 100.1 km for every 100 km driven. This is within the commonly quoted 3 % tolerance.
Full comparison
| Measurement | 265/70R17 | 265/65R18 | Difference |
|---|---|---|---|
| Section width | 265 mm | 265 mm | 0 mm |
| Sidewall height | 185.5 mm | 172.3 mm | -13.2 mm |
| Rim diameter | 17" | 18" | +1.0" |
| Overall diameter | 802.8 mm (31.61") | 801.7 mm (31.56") | -1.1 mm (-0.14 %) |
| Static circumference | 2522 mm | 2519 mm | -3 mm |
| Rolling circumference (ETRTO) | 2449 mm | 2445 mm | -3 mm |
| Revs per km | 408 | 409 | +1 |
| Ride height | -0.5 mm | ||
| Inch equivalent | 31.6×10.4R17 | 31.6×10.4R18 | |
| Approved rim widths (approx.) | 7.5″–9″ | 7.5″–9″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 39.9 | 49.9 | 59.9 | 79.9 | 99.9 | 109.8 |
| Error (km/h) | -0.1 | -0.1 | -0.1 | -0.1 | -0.1 | -0.2 |
Assumes the speedo was accurate on 265/70R17. Odometer records 100.1 km for every 100 km actually driven.
- The 265/65R18 is 1.1 mm (0.14 %) smaller in diameter, so your speedo will read high and your odometer will over-record distance.
- Rim diameter changes from 17" to 18", so new wheels are required.
Is 265/65R18 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -1.1 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 99.9 km/h (over-read 0.1 km/h; ADR 18 allows up to 14.0 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 265/65R18 instead of 265/70R17?
Overall diameter changes by -1.1 mm (-0.14 %). That is within the usual 3 % rule of thumb, so it is generally an acceptable swap provided the load index and speed rating meet your tyre placard and the tyre suits your rim width. 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 265/65R18?
Your speedo will read high by about 0.14 %. At an indicated 100 km/h you would actually be travelling 99.9 km/h, and at 110 km/h about 109.8 km/h.
What is the rolling circumference of 265/65R18?
Static circumference is 2519 mm; the ETRTO rolling circumference under load is about 2445 mm, which is 409 revolutions per kilometre.
265/65R18 in inches
265/65R18 is approximately 31.6×10.4R18: 31.6" tall, 10.4" wide, on a 18" rim, with a 6.8" sidewall.
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