155/55R15 vs 155/60R15
Going from one to the other changes the overall height by +2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/55R15 | 155/60R15 | Change |
|---|---|---|---|
| Overall height | 21.7" | 22.3" | +2.8 % |
| Sidewall | 3.36" | 3.66" | +9.1 % |
| Section width | 155 mm | 155 mm | 0.0 % |
| Circumference | 68.2" | 70.1" | +2.8 % |
| Revs per mile | 929 | 903 | -2.8 % |
| Axle height | 10.86" | 11.16" | +7.8 mm |
| Approved rim width | 4–5.5" | 4–5.5" | overlap 4–5.5" |
Both are approved on a rim 4" 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 155/55R15. Fit 155/60R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.5 mph | +2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,281 on the road, so it under-counts by 281. At a true 70 mph the first turns 1084 times a minute, the second 1054.