225/50R16 vs 205/55R16
205/55R16 has an overall diameter of 631.9 mm (24.88") compared with 631.4 mm (24.86") for 225/50R16, a difference of +0.5 mm (+0.08 %). The sidewall changes by +0.3 mm, section width by -20 mm and ride height by +0.3 mm. Using the ETRTO rolling circumference, 225/50R16 turns 519 times per kilometre and 205/55R16 turns 519 times. With 205/55R16 fitted to a car calibrated for 225/50R16, an indicated 100 km/h is a true 100.1 km/h, and the odometer records 99.9 km for every 100 km driven. This is within the commonly quoted 3 % tolerance.
Full comparison
| Measurement | 225/50R16 | 205/55R16 | Difference |
|---|---|---|---|
| Section width | 225 mm | 205 mm | -20 mm |
| Sidewall height | 112.5 mm | 112.8 mm | +0.3 mm |
| Rim diameter | 16" | 16" | 0.0" |
| Overall diameter | 631.4 mm (24.86") | 631.9 mm (24.88") | +0.5 mm (+0.08 %) |
| Static circumference | 1984 mm | 1985 mm | +2 mm |
| Rolling circumference (ETRTO) | 1926 mm | 1927 mm | +2 mm |
| Revs per km | 519 | 519 | 0 |
| Ride height | +0.3 mm | ||
| Inch equivalent | 24.9×8.9R16 | 24.9×8.1R16 | |
| Approved rim widths (approx.) | 6″–8″ | 5.5″–7.5″ |
Speedometer error
| Speedo reads | 40 | 50 | 60 | 80 | 100 | 110 |
|---|---|---|---|---|---|---|
| Actual speed (km/h) | 40.0 | 50.0 | 60.0 | 80.1 | 100.1 | 110.1 |
| Error (km/h) | +0.0 | +0.0 | +0.0 | +0.1 | +0.1 | +0.1 |
Assumes the speedo was accurate on 225/50R16. Odometer records 99.9 km for every 100 km actually driven.
- The 205/55R16 is 0.5 mm (0.08 %) larger in diameter, so your speedo will read low and your odometer will under-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.
Is 205/55R16 legal in Australia? Within limits, verify speedo
| Overall diameter (VSB 14 LS 4.2.4) Diameter change of +0.5 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 larger tyre makes the speedo read lower: at an indicated 100 km/h you would be doing 100.1 km/h. ADR 18 requires the speedo never to read below true speed, but factory speedos typically over-read by 2-6 %, so a 0.1 % 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 205/55R16 instead of 225/50R16?
Overall diameter changes by +0.5 mm (+0.08 %). 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 205/55R16?
Your speedo will read low by about 0.08 %. At an indicated 100 km/h you would actually be travelling 100.1 km/h, and at 110 km/h about 110.1 km/h.
What is the rolling circumference of 205/55R16?
Static circumference is 1985 mm; the ETRTO rolling circumference under load is about 1927 mm, which is 519 revolutions per kilometre.
205/55R16 in inches
205/55R16 is approximately 24.9×8.1R16: 24.9" tall, 8.1" wide, on a 16" rim, with a 4.4" sidewall.
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