185/70R17 vs 205/60R17
Going from one to the other changes the overall height by -1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/70R17 | 205/60R17 | Change |
|---|---|---|---|
| Overall height | 27.2" | 26.7" | -1.9 % |
| Sidewall | 5.10" | 4.84" | -5.0 % |
| Section width | 185 mm | 205 mm | +10.8 % |
| Circumference | 85.4" | 83.8" | -1.9 % |
| Revs per mile | 742 | 756 | +1.9 % |
| Axle height | 13.60" | 13.34" | -6.5 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 185/70R17. Fit 205/60R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,812 on the road, so it over-counts by 188. At a true 70 mph the first turns 865 times a minute, the second 882.