185/85R13 vs 205/75R13
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/85R13 | 205/75R13 | Change |
|---|---|---|---|
| Overall height | 25.4" | 25.1" | -1.1 % |
| Sidewall | 6.19" | 6.05" | -2.2 % |
| Section width | 185 mm | 205 mm | +10.8 % |
| Circumference | 79.7" | 78.9" | -1.1 % |
| Revs per mile | 795 | 803 | +1.1 % |
| Axle height | 12.69" | 12.55" | -3.5 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 185/85R13. Fit 205/75R13 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,891 on the road, so it over-counts by 109. At a true 70 mph the first turns 927 times a minute, the second 937.