165/85R13 vs 165/80R13
Going from one to the other changes the overall height by -2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 165/85R13 | 165/80R13 | Change |
|---|---|---|---|
| Overall height | 24.0" | 23.4" | -2.7 % |
| Sidewall | 5.52" | 5.20" | -5.9 % |
| Section width | 165 mm | 165 mm | 0.0 % |
| Circumference | 75.5" | 73.5" | -2.7 % |
| Revs per mile | 839 | 862 | +2.7 % |
| Axle height | 12.02" | 11.70" | -8.3 mm |
| Approved rim width | 4.5–6" | 4.5–6" | overlap 4.5–6" |
Both are approved on a rim 4.5" to 6" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 165/85R13. Fit 165/80R13 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.1 mph | -1.9 |
| 90 mph | 87.6 mph | -2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,730 on the road, so it over-counts by 270. At a true 70 mph the first turns 979 times a minute, the second 1006.