305/40R22 vs 275/50R20
275/50R20 has an overall diameter of 783.0 mm (30.83") compared with 802.8 mm (31.61") for 305/40R22, a difference of -19.8 mm (-2.47 %). The sidewall changes by +15.5 mm, section width by -30 mm and ride height by -9.9 mm. Using the ETRTO rolling circumference, 305/40R22 turns 408 times per kilometre and 275/50R20 turns 419 times. With 275/50R20 fitted to a car calibrated for 305/40R22, an indicated 100 km/h is a true 97.5 km/h, and the odometer records 102.5 km for every 100 km driven. This is close to the commonly quoted 3 % tolerance, so check clearance and local rules.
Full comparison
| Measurement | 305/40R22 | 275/50R20 | Difference |
|---|---|---|---|
| Section width | 305 mm | 275 mm | -30 mm |
| Sidewall height | 122.0 mm | 137.5 mm | +15.5 mm |
| Rim diameter | 22" | 20" | -2.0" |
| Overall diameter | 802.8 mm (31.61") | 783.0 mm (30.83") | -19.8 mm (-2.47 %) |
| Static circumference | 2522 mm | 2460 mm | -62 mm |
| Rolling circumference (ETRTO) | 2449 mm | 2388 mm | -60 mm |
| Revs per km | 408 | 419 | +10 |
| Ride height | -9.9 mm | ||
| Inch equivalent | 31.6x12R22 | 30.8×10.8R20 | |
| Approved rim widths (approx.) | 10.5″–12″ | 7.5″–9.5″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 39.0 | 48.8 | 58.5 | 78.0 | 97.5 | 107.3 |
| Error (km/h) | -1.0 | -1.2 | -1.5 | -2.0 | -2.5 | -2.7 |
Assumes the speedo was accurate on 305/40R22. Odometer records 102.5 km for every 100 km actually driven.
- The 275/50R20 is 19.8 mm (2.47 %) smaller in diameter, so your speedo will read high and your odometer will over-record distance.
- Section width changes by -30 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 275/50R20 legal in Australia? More info needed
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of -19.8 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 97.5 km/h (over-read 2.5 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 275/50R20 instead of 305/40R22?
Overall diameter changes by -19.8 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 275/50R20?
Your speedo will read high by about 2.47 %. At an indicated 100 km/h you would actually be travelling 97.5 km/h, and at 110 km/h about 107.3 km/h.
What is the rolling circumference of 275/50R20?
Static circumference is 2460 mm; the ETRTO rolling circumference under load is about 2388 mm, which is 419 revolutions per kilometre.
275/50R20 in inches
275/50R20 is approximately 30.8×10.8R20: 30.8" tall, 10.8" wide, on a 20" rim, with a 5.4" sidewall.
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