205/75R15 vs 185/85R15
Going from one to the other changes the overall height by +1.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/75R15 | 185/85R15 | Change |
|---|---|---|---|
| Overall height | 27.1" | 27.4" | +1.0 % |
| Sidewall | 6.05" | 6.19" | +2.3 % |
| Section width | 205 mm | 185 mm | -9.8 % |
| Circumference | 85.2" | 86.0" | +1.0 % |
| Revs per mile | 744 | 737 | -1.0 % |
| Axle height | 13.55" | 13.69" | +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 205/75R15. Fit 185/85R15 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 10,102 on the road, so it under-counts by 102. At a true 70 mph the first turns 868 times a minute, the second 859.
What drivers reported
205/75R15 carries 84 complaints. Nobody has filed one naming 185/85R15.