235/55R18 vs 275/45R19
275/45R19 has an overall diameter of 730.1 mm (28.74") compared with 715.7 mm (28.18") for 235/55R18, a difference of +14.4 mm (+2.01 %). The sidewall changes by -5.5 mm, section width by +40 mm and ride height by +7.2 mm. Using the ETRTO rolling circumference, 235/55R18 turns 458 times per kilometre and 275/45R19 turns 449 times. With 275/45R19 fitted to a car calibrated for 235/55R18, an indicated 100 km/h is a true 102 km/h, and the odometer records 98 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 235/55R18 | 275/45R19 | Difference |
|---|---|---|---|
| Section width | 235 mm | 275 mm | +40 mm |
| Sidewall height | 129.3 mm | 123.8 mm | -5.5 mm |
| Rim diameter | 18" | 19" | +1.0" |
| Overall diameter | 715.7 mm (28.18") | 730.1 mm (28.74") | +14.4 mm (+2.01 %) |
| Static circumference | 2248 mm | 2294 mm | +45 mm |
| Rolling circumference (ETRTO) | 2183 mm | 2227 mm | +44 mm |
| Revs per km | 458 | 449 | -9 |
| Ride height | +7.2 mm | ||
| Inch equivalent | 28.2×9.3R18 | 28.7×10.8R19 | |
| Approved rim widths (approx.) | 6.5″–8.5″ | 8.5″–10″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 40.8 | 51.0 | 61.2 | 81.6 | 102.0 | 112.2 |
| Error (km/h) | +0.8 | +1.0 | +1.2 | +1.6 | +2.0 | +2.2 |
Assumes the speedo was accurate on 235/55R18. Odometer records 98.0 km for every 100 km actually driven.
- The 275/45R19 is 14.4 mm (2.01 %) larger in diameter, so your speedo will read low and your odometer will under-record distance.
- Section width changes by +40 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 19", so new wheels are required.
Is 275/45R19 legal in Australia? Within limits, verify speedo
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of +14.4 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 larger tyre makes the speedo read lower: at an indicated 100 km/h you would be doing 102.0 km/h. ADR 18 requires the speedo never to read below true speed, but factory speedos typically over-read by 2-6 %, so a 2.0 % 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 275/45R19 instead of 235/55R18?
Overall diameter changes by +14.4 mm (+2.01 %). 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 275/45R19?
Your speedo will read low by about 2.01 %. At an indicated 100 km/h you would actually be travelling 102 km/h, and at 110 km/h about 112.2 km/h.
What is the rolling circumference of 275/45R19?
Static circumference is 2294 mm; the ETRTO rolling circumference under load is about 2227 mm, which is 449 revolutions per kilometre.
275/45R19 in inches
275/45R19 is approximately 28.7×10.8R19: 28.7" tall, 10.8" wide, on a 19" rim, with a 4.9" sidewall.
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