185/50R17 vs 185/45R17
Going from one to the other changes the overall height by -3.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/50R17 | 185/45R17 | Change |
|---|---|---|---|
| Overall height | 24.3" | 23.6" | -3.0 % |
| Sidewall | 3.64" | 3.28" | -10.0 % |
| Section width | 185 mm | 185 mm | 0.0 % |
| Circumference | 76.3" | 74.0" | -3.0 % |
| Revs per mile | 831 | 856 | +3.0 % |
| Axle height | 12.14" | 11.78" | -9.3 mm |
| Approved rim width | 5–6.5" | 5–6.5" | overlap 5–6.5" |
Both are approved on a rim 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 185/50R17. Fit 185/45R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.5 mph | -1.5 |
| 70 mph | 67.9 mph | -2.1 |
| 90 mph | 87.3 mph | -2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,700 on the road, so it over-counts by 300. At a true 70 mph the first turns 969 times a minute, the second 999.