185/55R16 vs 205/50R16
Going from one to the other changes the overall height by +0.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/55R16 | 205/50R16 | Change |
|---|---|---|---|
| Overall height | 24.0" | 24.1" | +0.2 % |
| Sidewall | 4.01" | 4.04" | +0.7 % |
| Section width | 185 mm | 205 mm | +10.8 % |
| Circumference | 75.4" | 75.6" | +0.2 % |
| Revs per mile | 840 | 838 | -0.2 % |
| Axle height | 12.01" | 12.04" | +0.8 mm |
| Approved rim width | 5–6.5" | 5.5–7.5" | overlap 5.5–6.5" |
Both are approved on a rim 5.5" to 6.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 185/55R16. Fit 205/50R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.1 mph | +0.1 |
| 70 mph | 70.2 mph | +0.2 |
| 90 mph | 90.2 mph | +0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,025 on the road, so it under-counts by 25. At a true 70 mph the first turns 980 times a minute, the second 978.