165/80R14 vs 165/85R14
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 | 165/80R14 | 165/85R14 | Change |
|---|---|---|---|
| Overall height | 24.4" | 25.0" | +2.7 % |
| Sidewall | 5.20" | 5.52" | +6.3 % |
| Section width | 165 mm | 165 mm | 0.0 % |
| Circumference | 76.6" | 78.7" | +2.7 % |
| Revs per mile | 827 | 805 | -2.7 % |
| Axle height | 12.20" | 12.52" | +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 165/80R14. Fit 165/85R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,266 on the road, so it under-counts by 266. At a true 70 mph the first turns 965 times a minute, the second 940.