155/65R15 vs 175/55R15
Going from one to the other changes the overall height by -1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/65R15 | 175/55R15 | Change |
|---|---|---|---|
| Overall height | 22.9" | 22.6" | -1.5 % |
| Sidewall | 3.97" | 3.79" | -4.5 % |
| Section width | 155 mm | 175 mm | +12.9 % |
| Circumference | 72.0" | 70.9" | -1.5 % |
| Revs per mile | 879 | 893 | +1.5 % |
| Axle height | 11.47" | 11.29" | -4.5 mm |
| Approved rim width | 4–5.5" | 5–6" | 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 155/65R15. Fit 175/55R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.6 mph | -1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,845 on the road, so it over-counts by 155. At a true 70 mph the first turns 1026 times a minute, the second 1042.