205/65R15 vs 185/75R15
Going from one to the other changes the overall height by +1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/65R15 | 185/75R15 | Change |
|---|---|---|---|
| Overall height | 25.5" | 25.9" | +1.7 % |
| Sidewall | 5.25" | 5.46" | +4.1 % |
| Section width | 205 mm | 185 mm | -9.8 % |
| Circumference | 80.1" | 81.4" | +1.7 % |
| Revs per mile | 791 | 778 | -1.7 % |
| Axle height | 12.75" | 12.96" | +5.5 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 205/65R15. Fit 185/75R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.5 mph | +1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,170 on the road, so it under-counts by 170. At a true 70 mph the first turns 923 times a minute, the second 908.
What drivers reported
205/65R15 carries 182 complaints. Nobody has filed one naming 185/75R15.