175/50R15 vs 155/60R15
Going from one to the other changes the overall height by +2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/50R15 | 155/60R15 | Change |
|---|---|---|---|
| Overall height | 21.9" | 22.3" | +2.0 % |
| Sidewall | 3.44" | 3.66" | +6.3 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 68.8" | 70.1" | +2.0 % |
| Revs per mile | 921 | 903 | -2.0 % |
| Axle height | 10.94" | 11.16" | +5.5 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 175/50R15. Fit 155/60R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.8 mph | +1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,198 on the road, so it under-counts by 198. At a true 70 mph the first turns 1075 times a minute, the second 1054.