205/70R15 vs 185/80R15
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 | 205/70R15 | 185/80R15 | Change |
|---|---|---|---|
| Overall height | 26.3" | 26.7" | +1.3 % |
| Sidewall | 5.65" | 5.83" | +3.1 % |
| Section width | 205 mm | 185 mm | -9.8 % |
| Circumference | 82.6" | 83.7" | +1.3 % |
| Revs per mile | 767 | 757 | -1.3 % |
| Axle height | 13.15" | 13.33" | +4.5 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 205/70R15. Fit 185/80R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,135 on the road, so it under-counts by 135. At a true 70 mph the first turns 895 times a minute, the second 883.
What drivers reported
205/70R15 carries 98 complaints. Nobody has filed one naming 185/80R15.