235/60R18 vs 225/65R17
225/65R17 has an overall diameter of 724.3 mm (28.52") compared with 739.2 mm (29.10") for 235/60R18, a difference of -14.9 mm (-2.02 %). The sidewall changes by +5.3 mm, section width by -10 mm and ride height by -7.5 mm. Using the ETRTO rolling circumference, 235/60R18 turns 444 times per kilometre and 225/65R17 turns 453 times. With 225/65R17 fitted to a car calibrated for 235/60R18, an indicated 100 km/h is a true 98 km/h, and the odometer records 102.1 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 235/60R18 | 225/65R17 | Difference |
|---|---|---|---|
| Section width | 235 mm | 225 mm | -10 mm |
| Sidewall height | 141.0 mm | 146.3 mm | +5.3 mm |
| Rim diameter | 18" | 17" | -1.0" |
| Overall diameter | 739.2 mm (29.10") | 724.3 mm (28.52") | -14.9 mm (-2.02 %) |
| Static circumference | 2322 mm | 2275 mm | -47 mm |
| Rolling circumference (ETRTO) | 2255 mm | 2209 mm | -45 mm |
| Revs per km | 444 | 453 | +9 |
| Ride height | -7.5 mm | ||
| Inch equivalent | 29.1×9.3R18 | 28.5×8.9R17 | |
| Approved rim widths (approx.) | 6.5″–8″ | 6″–7.5″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 39.2 | 49.0 | 58.8 | 78.4 | 98.0 | 107.8 |
| Error (km/h) | -0.8 | -1.0 | -1.2 | -1.6 | -2.0 | -2.2 |
Assumes the speedo was accurate on 235/60R18. Odometer records 102.1 km for every 100 km actually driven.
- The 225/65R17 is 14.9 mm (2.02 %) 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 18" to 17", so new wheels are required.
Is 225/65R17 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -14.9 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 98.0 km/h (over-read 2.0 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 225/65R17 instead of 235/60R18?
Overall diameter changes by -14.9 mm (-2.02 %). 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 225/65R17?
Your speedo will read high by about 2.02 %. At an indicated 100 km/h you would actually be travelling 98 km/h, and at 110 km/h about 107.8 km/h.
What is the rolling circumference of 225/65R17?
Static circumference is 2275 mm; the ETRTO rolling circumference under load is about 2209 mm, which is 453 revolutions per kilometre.
225/65R17 in inches
225/65R17 is approximately 28.5×8.9R17: 28.5" tall, 8.9" wide, on a 17" rim, with a 5.8" sidewall.
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