165/80R16 vs 165/85R16
Going from one to the other changes the overall height by +2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 165/80R16 | 165/85R16 | Change |
|---|---|---|---|
| Overall height | 26.4" | 27.0" | +2.5 % |
| Sidewall | 5.20" | 5.52" | +6.3 % |
| Section width | 165 mm | 165 mm | 0.0 % |
| Circumference | 82.9" | 85.0" | +2.5 % |
| Revs per mile | 764 | 746 | -2.5 % |
| Axle height | 13.20" | 13.52" | +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 165/80R16. Fit 165/85R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.7 mph | +1.7 |
| 90 mph | 92.2 mph | +2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,246 on the road, so it under-counts by 246. At a true 70 mph the first turns 891 times a minute, the second 870.