195/80R13 vs 185/85R13
Going from one to the other changes the overall height by +0.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/80R13 | 185/85R13 | Change |
|---|---|---|---|
| Overall height | 25.3" | 25.4" | +0.4 % |
| Sidewall | 6.14" | 6.19" | +0.8 % |
| Section width | 195 mm | 185 mm | -5.1 % |
| Circumference | 79.4" | 79.7" | +0.4 % |
| Revs per mile | 798 | 795 | -0.4 % |
| Axle height | 12.64" | 12.69" | +1.3 mm |
| Approved rim width | 5.5–7" | 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 195/80R13. Fit 185/85R13 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.2 mph | +0.2 |
| 70 mph | 70.3 mph | +0.3 |
| 90 mph | 90.4 mph | +0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,039 on the road, so it under-counts by 39. At a true 70 mph the first turns 931 times a minute, the second 927.