185/80R15 vs 205/70R15
Going from one to the other changes the overall height by -1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/80R15 | 205/70R15 | Change |
|---|---|---|---|
| Overall height | 26.7" | 26.3" | -1.3 % |
| Sidewall | 5.83" | 5.65" | -3.0 % |
| Section width | 185 mm | 205 mm | +10.8 % |
| Circumference | 83.7" | 82.6" | -1.3 % |
| Revs per mile | 757 | 767 | +1.3 % |
| Axle height | 13.33" | 13.15" | -4.5 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 185/80R15. Fit 205/70R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.8 mph | -1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,867 on the road, so it over-counts by 133. At a true 70 mph the first turns 883 times a minute, the second 895.
What drivers reported
Nobody has filed a complaint naming 185/80R15. 205/70R15 carries 98.