205/60R15 vs 185/65R15
Going from one to the other changes the overall height by -0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/60R15 | 185/65R15 | Change |
|---|---|---|---|
| Overall height | 24.7" | 24.5" | -0.9 % |
| Sidewall | 4.84" | 4.73" | -2.2 % |
| Section width | 205 mm | 185 mm | -9.8 % |
| Circumference | 77.6" | 76.9" | -0.9 % |
| Revs per mile | 817 | 824 | +0.9 % |
| Axle height | 12.34" | 12.23" | -2.8 mm |
| Approved rim width | 5.5–7.5" | 5–6.5" | 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 205/60R15. Fit 185/65R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.4 mph | -0.6 |
| 90 mph | 89.2 mph | -0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,912 on the road, so it over-counts by 88. At a true 70 mph the first turns 953 times a minute, the second 962.