185/50R15 vs 175/50R15
Going from one to the other changes the overall height by -1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/50R15 | 175/50R15 | Change |
|---|---|---|---|
| Overall height | 22.3" | 21.9" | -1.8 % |
| Sidewall | 3.64" | 3.44" | -5.4 % |
| Section width | 185 mm | 175 mm | -5.4 % |
| Circumference | 70.0" | 68.8" | -1.8 % |
| Revs per mile | 905 | 921 | +1.8 % |
| Axle height | 11.14" | 10.94" | -5.0 mm |
| Approved rim width | 5–6.5" | 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 185/50R15. Fit 175/50R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,823 on the road, so it over-counts by 177. At a true 70 mph the first turns 1056 times a minute, the second 1075.
What drivers reported
185/50R15 carries 2 complaints. Nobody has filed one naming 175/50R15.