195/45R15 vs 175/50R15
Going from one to the other changes the overall height by -0.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/45R15 | 175/50R15 | Change |
|---|---|---|---|
| Overall height | 21.9" | 21.9" | -0.1 % |
| Sidewall | 3.45" | 3.44" | -0.3 % |
| Section width | 195 mm | 175 mm | -10.3 % |
| Circumference | 68.8" | 68.8" | -0.1 % |
| Revs per mile | 921 | 921 | +0.1 % |
| Axle height | 10.95" | 10.94" | -0.3 mm |
| Approved rim width | 5.5–7" | 5–6" | overlap 5.5–6" |
Both are approved on a rim 5.5" to 6" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 195/45R15. Fit 175/50R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.0 mph | -0.0 |
| 50 mph | 50.0 mph | -0.0 |
| 70 mph | 69.9 mph | -0.1 |
| 90 mph | 89.9 mph | -0.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,991 on the road, so it over-counts by 9. At a true 70 mph the first turns 1074 times a minute, the second 1075.