185/70R15 vs 205/65R15
Going from one to the other changes the overall height by +1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/70R15 | 205/65R15 | Change |
|---|---|---|---|
| Overall height | 25.2" | 25.5" | +1.2 % |
| Sidewall | 5.10" | 5.25" | +2.9 % |
| Section width | 185 mm | 205 mm | +10.8 % |
| Circumference | 79.2" | 80.1" | +1.2 % |
| Revs per mile | 800 | 791 | -1.2 % |
| Axle height | 12.60" | 12.75" | +3.8 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 185/70R15. Fit 205/65R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.1 mph | +1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,117 on the road, so it under-counts by 117. At a true 70 mph the first turns 934 times a minute, the second 923.
What drivers reported
Nobody has filed a complaint naming 185/70R15. 205/65R15 carries 182.