185/75R15 vs 205/65R15
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 | 185/75R15 | 205/65R15 | Change |
|---|---|---|---|
| Overall height | 25.9" | 25.5" | -1.7 % |
| Sidewall | 5.46" | 5.25" | -4.0 % |
| Section width | 185 mm | 205 mm | +10.8 % |
| Circumference | 81.4" | 80.1" | -1.7 % |
| Revs per mile | 778 | 791 | +1.7 % |
| Axle height | 12.96" | 12.75" | -5.5 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 185/75R15. Fit 205/65R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,833 on the road, so it over-counts by 167. At a true 70 mph the first turns 908 times a minute, the second 923.
What drivers reported
Nobody has filed a complaint naming 185/75R15. 205/65R15 carries 182.