175/65R15 vs 155/75R15
Going from one to the other changes the overall height by +0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/65R15 | 155/75R15 | Change |
|---|---|---|---|
| Overall height | 24.0" | 24.2" | +0.8 % |
| Sidewall | 4.48" | 4.58" | +2.2 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 75.3" | 75.9" | +0.8 % |
| Revs per mile | 842 | 835 | -0.8 % |
| Axle height | 11.98" | 12.08" | +2.5 mm |
| Approved rim width | 5–6" | 4–5.5" | overlap 5–5.5" |
Both are approved on a rim 5" to 5.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 175/65R15. Fit 155/75R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.7 mph | +0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,082 on the road, so it under-counts by 82. At a true 70 mph the first turns 982 times a minute, the second 974.
What drivers reported
175/65R15 carries 6 complaints. Nobody has filed one naming 155/75R15.