205/75R17 vs 185/85R17
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 | 205/75R17 | 185/85R17 | Change |
|---|---|---|---|
| Overall height | 29.1" | 29.4" | +0.9 % |
| Sidewall | 6.05" | 6.19" | +2.3 % |
| Section width | 205 mm | 185 mm | -9.8 % |
| Circumference | 91.4" | 92.3" | +0.9 % |
| Revs per mile | 693 | 686 | -0.9 % |
| Axle height | 14.55" | 14.69" | +3.5 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 205/75R17. Fit 185/85R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.7 mph | +0.7 |
| 90 mph | 90.9 mph | +0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,095 on the road, so it under-counts by 95. At a true 70 mph the first turns 808 times a minute, the second 801.