175/55R15 vs 155/65R15
Going from one to the other changes the overall height by +1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/55R15 | 155/65R15 | Change |
|---|---|---|---|
| Overall height | 22.6" | 22.9" | +1.6 % |
| Sidewall | 3.79" | 3.97" | +4.7 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 70.9" | 72.0" | +1.6 % |
| Revs per mile | 893 | 879 | -1.6 % |
| Axle height | 11.29" | 11.47" | +4.5 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 175/55R15. Fit 155/65R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.1 mph | +1.1 |
| 90 mph | 91.4 mph | +1.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,157 on the road, so it under-counts by 157. At a true 70 mph the first turns 1042 times a minute, the second 1026.