275/40R22 vs 255/50R20
255/50R20 has an overall diameter of 763.0 mm (30.04") compared with 778.8 mm (30.66") for 275/40R22, a difference of -15.8 mm (-2.03 %). The sidewall changes by +17.5 mm, section width by -20 mm and ride height by -7.9 mm. Using the ETRTO rolling circumference, 275/40R22 turns 421 times per kilometre and 255/50R20 turns 430 times. With 255/50R20 fitted to a car calibrated for 275/40R22, 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 | 275/40R22 | 255/50R20 | Difference |
|---|---|---|---|
| Section width | 275 mm | 255 mm | -20 mm |
| Sidewall height | 110.0 mm | 127.5 mm | +17.5 mm |
| Rim diameter | 22" | 20" | -2.0" |
| Overall diameter | 778.8 mm (30.66") | 763.0 mm (30.04") | -15.8 mm (-2.03 %) |
| Static circumference | 2447 mm | 2397 mm | -50 mm |
| Rolling circumference (ETRTO) | 2375 mm | 2327 mm | -48 mm |
| Revs per km | 421 | 430 | +9 |
| Ride height | -7.9 mm | ||
| Inch equivalent | 30.7×10.8R22 | 30x10R20 | |
| Approved rim widths (approx.) | 9″–10.5″ | 7″–9″ |
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 275/40R22. Odometer records 102.1 km for every 100 km actually driven.
- The 255/50R20 is 15.8 mm (2.03 %) smaller in diameter, so your speedo will read high and your odometer will over-record distance.
- Section width changes by -20 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 22" to 20", so new wheels are required.
Is 255/50R20 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -15.8 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 255/50R20 instead of 275/40R22?
Overall diameter changes by -15.8 mm (-2.03 %). 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 255/50R20?
Your speedo will read high by about 2.03 %. 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 255/50R20?
Static circumference is 2397 mm; the ETRTO rolling circumference under load is about 2327 mm, which is 430 revolutions per kilometre.
255/50R20 in inches
255/50R20 is approximately 30x10R20: 30.0" tall, 10.0" wide, on a 20" rim, with a 5.0" sidewall.
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