185/65R15 vs 205/55R15
Going from one to the other changes the overall height by -2.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/65R15 | 205/55R15 | Change |
|---|---|---|---|
| Overall height | 24.5" | 23.9" | -2.4 % |
| Sidewall | 4.73" | 4.44" | -6.2 % |
| Section width | 185 mm | 205 mm | +10.8 % |
| Circumference | 76.9" | 75.0" | -2.4 % |
| Revs per mile | 824 | 845 | +2.4 % |
| Axle height | 12.23" | 11.94" | -7.5 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 185/65R15. Fit 205/55R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.3 mph | -1.7 |
| 90 mph | 87.8 mph | -2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,759 on the road, so it over-counts by 241. At a true 70 mph the first turns 962 times a minute, the second 985.