255/35R18 vs 245/35R19
245/35R19 has an overall diameter of 654.1 mm (25.75") compared with 635.7 mm (25.03") for 255/35R18, a difference of +18.4 mm (+2.89 %). The sidewall changes by -3.5 mm, section width by -10 mm and ride height by +9.2 mm. Using the ETRTO rolling circumference, 255/35R18 turns 516 times per kilometre and 245/35R19 turns 501 times. With 245/35R19 fitted to a car calibrated for 255/35R18, an indicated 100 km/h is a true 102.9 km/h, and the odometer records 97.2 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 255/35R18 | 245/35R19 | Difference |
|---|---|---|---|
| Section width | 255 mm | 245 mm | -10 mm |
| Sidewall height | 89.3 mm | 85.8 mm | -3.5 mm |
| Rim diameter | 18" | 19" | +1.0" |
| Overall diameter | 635.7 mm (25.03") | 654.1 mm (25.75") | +18.4 mm (+2.89 %) |
| Static circumference | 1997 mm | 2055 mm | +58 mm |
| Rolling circumference (ETRTO) | 1939 mm | 1995 mm | +56 mm |
| Revs per km | 516 | 501 | -15 |
| Ride height | +9.2 mm | ||
| Inch equivalent | 25x10R18 | 25.8×9.6R19 | |
| Approved rim widths (approx.) | 8.5″–10″ | 8″–9.5″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 41.2 | 51.4 | 61.7 | 82.3 | 102.9 | 113.2 |
| Error (km/h) | +1.2 | +1.4 | +1.7 | +2.3 | +2.9 | +3.2 |
Assumes the speedo was accurate on 255/35R18. Odometer records 97.2 km for every 100 km actually driven.
- The 245/35R19 is 18.4 mm (2.89 %) 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.
- Rim diameter changes from 18" to 19", so new wheels are required.
Is 245/35R19 legal in Australia? Needs certification
| Overall diameter (VSB 14 LS 4.2.4) 245/35R19 is 18.4 mm larger than 255/35R18; 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 245/35R19 instead of 255/35R18?
Overall diameter changes by +18.4 mm (+2.89 %). 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 245/35R19?
Your speedo will read low by about 2.89 %. 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 245/35R19?
Static circumference is 2055 mm; the ETRTO rolling circumference under load is about 1995 mm, which is 501 revolutions per kilometre.
245/35R19 in inches
245/35R19 is approximately 25.8×9.6R19: 25.8" tall, 9.6" wide, on a 19" rim, with a 3.4" sidewall.
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