255/55R20 vs 265/50R20
265/50R20 has an overall diameter of 773.0 mm (30.43") compared with 788.5 mm (31.04") for 255/55R20, a difference of -15.5 mm (-1.97 %). The sidewall changes by -7.7 mm, section width by +10 mm and ride height by -7.7 mm. Using the ETRTO rolling circumference, 255/55R20 turns 416 times per kilometre and 265/50R20 turns 424 times. With 265/50R20 fitted to a car calibrated for 255/55R20, an indicated 100 km/h is a true 98 km/h, and the odometer records 102 km for every 100 km driven. This is within the commonly quoted 3 % tolerance.
Full comparison
| Measurement | 255/55R20 | 265/50R20 | Difference |
|---|---|---|---|
| Section width | 255 mm | 265 mm | +10 mm |
| Sidewall height | 140.3 mm | 132.5 mm | -7.7 mm |
| Rim diameter | 20" | 20" | 0.0" |
| Overall diameter | 788.5 mm (31.04") | 773.0 mm (30.43") | -15.5 mm (-1.97 %) |
| Static circumference | 2477 mm | 2428 mm | -49 mm |
| Rolling circumference (ETRTO) | 2405 mm | 2358 mm | -47 mm |
| Revs per km | 416 | 424 | +8 |
| Ride height | -7.7 mm | ||
| Inch equivalent | 31x10R20 | 30.4×10.4R20 | |
| Approved rim widths (approx.) | 7″–9″ | 7.5″–9.5″ |
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 255/55R20. Odometer records 102.0 km for every 100 km actually driven.
- The 265/50R20 is 15.5 mm (1.97 %) 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.
Is 265/50R20 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -15.5 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 265/50R20 instead of 255/55R20?
Overall diameter changes by -15.5 mm (-1.97 %). That is within the usual 3 % rule of thumb, so it is generally an acceptable swap provided the load index and speed rating meet your tyre placard and the tyre suits your rim width. 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 265/50R20?
Your speedo will read high by about 1.97 %. 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 265/50R20?
Static circumference is 2428 mm; the ETRTO rolling circumference under load is about 2358 mm, which is 424 revolutions per kilometre.
265/50R20 in inches
265/50R20 is approximately 30.4×10.4R20: 30.4" tall, 10.4" wide, on a 20" rim, with a 5.2" sidewall.
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