245/40R17 vs 235/45R17
235/45R17 has an overall diameter of 643.3 mm (25.33") compared with 627.8 mm (24.72") for 245/40R17, a difference of +15.5 mm (+2.47 %). The sidewall changes by +7.8 mm, section width by -10 mm and ride height by +7.8 mm. Using the ETRTO rolling circumference, 245/40R17 turns 522 times per kilometre and 235/45R17 turns 510 times. With 235/45R17 fitted to a car calibrated for 245/40R17, an indicated 100 km/h is a true 102.5 km/h, and the odometer records 97.6 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 245/40R17 | 235/45R17 | Difference |
|---|---|---|---|
| Section width | 245 mm | 235 mm | -10 mm |
| Sidewall height | 98.0 mm | 105.8 mm | +7.8 mm |
| Rim diameter | 17" | 17" | 0.0" |
| Overall diameter | 627.8 mm (24.72") | 643.3 mm (25.33") | +15.5 mm (+2.47 %) |
| Static circumference | 1972 mm | 2021 mm | +49 mm |
| Rolling circumference (ETRTO) | 1915 mm | 1962 mm | +47 mm |
| Revs per km | 522 | 510 | -13 |
| Ride height | +7.8 mm | ||
| Inch equivalent | 24.7×9.6R17 | 25.3×9.3R17 | |
| Approved rim widths (approx.) | 8″–9.5″ | 7.5″–9″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 41.0 | 51.2 | 61.5 | 82.0 | 102.5 | 112.7 |
| Error (km/h) | +1.0 | +1.2 | +1.5 | +2.0 | +2.5 | +2.7 |
Assumes the speedo was accurate on 245/40R17. Odometer records 97.6 km for every 100 km actually driven.
- The 235/45R17 is 15.5 mm (2.47 %) larger in diameter, so your speedo will read low and your odometer will under-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.
Is 235/45R17 legal in Australia? Needs certification
| Overall diameter (VSB 14 LS 4.2.4) 235/45R17 is 15.5 mm larger than 245/40R17; 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 102.5 km/h. ADR 18 requires the speedo never to read below true speed, but factory speedos typically over-read by 2-6 %, so a 2.5 % 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 235/45R17 instead of 245/40R17?
Overall diameter changes by +15.5 mm (+2.47 %). 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 235/45R17?
Your speedo will read low by about 2.47 %. At an indicated 100 km/h you would actually be travelling 102.5 km/h, and at 110 km/h about 112.7 km/h.
What is the rolling circumference of 235/45R17?
Static circumference is 2021 mm; the ETRTO rolling circumference under load is about 1962 mm, which is 510 revolutions per kilometre.
235/45R17 in inches
235/45R17 is approximately 25.3×9.3R17: 25.3" tall, 9.3" wide, on a 17" rim, with a 4.2" sidewall.
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