275/70R16 vs 275/65R18
275/65R18 has an overall diameter of 814.7 mm (32.07") compared with 791.4 mm (31.16") for 275/70R16, a difference of +23.3 mm (+2.94 %). The sidewall changes by -13.7 mm, section width by 0 mm and ride height by +11.7 mm. Using the ETRTO rolling circumference, 275/70R16 turns 414 times per kilometre and 275/65R18 turns 402 times. With 275/65R18 fitted to a car calibrated for 275/70R16, 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 | 275/70R16 | 275/65R18 | Difference |
|---|---|---|---|
| Section width | 275 mm | 275 mm | 0 mm |
| Sidewall height | 192.5 mm | 178.8 mm | -13.7 mm |
| Rim diameter | 16" | 18" | +2.0" |
| Overall diameter | 791.4 mm (31.16") | 814.7 mm (32.07") | +23.3 mm (+2.94 %) |
| Static circumference | 2486 mm | 2559 mm | +73 mm |
| Rolling circumference (ETRTO) | 2414 mm | 2485 mm | +71 mm |
| Revs per km | 414 | 402 | -12 |
| Ride height | +11.7 mm | ||
| Inch equivalent | 31.2×10.8R16 | 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) | 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 275/70R16. Odometer records 97.1 km for every 100 km actually driven.
- The 275/65R18 is 23.3 mm (2.94 %) larger in diameter, so your speedo will read low and your odometer will under-record distance.
- Rim diameter changes from 16" to 18", so new wheels are required.
Is 275/65R18 legal in Australia? Needs certification
| Overall diameter (VSB 14 LS 4.2.4) 275/65R18 is 23.3 mm larger than 275/70R16; 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 275/65R18 instead of 275/70R16?
Overall diameter changes by +23.3 mm (+2.94 %). 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 low by about 2.94 %. 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 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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