185/45R14 vs 165/55R14
Going from one to the other changes the overall height by +2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/45R14 | 165/55R14 | Change |
|---|---|---|---|
| Overall height | 20.6" | 21.1" | +2.9 % |
| Sidewall | 3.28" | 3.57" | +9.0 % |
| Section width | 185 mm | 165 mm | -10.8 % |
| Circumference | 64.6" | 66.4" | +2.9 % |
| Revs per mile | 981 | 954 | -2.9 % |
| Axle height | 10.28" | 10.57" | +7.5 mm |
| Approved rim width | 5–6.5" | 4.5–6" | overlap 5–6" |
Both are approved on a rim 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 185/45R14. Fit 165/55R14 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,287 on the road, so it under-counts by 287. At a true 70 mph the first turns 1145 times a minute, the second 1113.