165/70R15 vs 155/75R15
Going from one to the other changes the overall height by +0.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 165/70R15 | 155/75R15 | Change |
|---|---|---|---|
| Overall height | 24.1" | 24.2" | +0.2 % |
| Sidewall | 4.55" | 4.58" | +0.6 % |
| Section width | 165 mm | 155 mm | -6.1 % |
| Circumference | 75.7" | 75.9" | +0.2 % |
| Revs per mile | 837 | 835 | -0.2 % |
| Axle height | 12.05" | 12.08" | +0.8 mm |
| Approved rim width | 4.5–6" | 4–5.5" | overlap 4.5–5.5" |
Both are approved on a rim 4.5" 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 165/70R15. Fit 155/75R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.1 mph | +0.1 |
| 70 mph | 70.2 mph | +0.2 |
| 90 mph | 90.2 mph | +0.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,025 on the road, so it under-counts by 25. At a true 70 mph the first turns 977 times a minute, the second 974.
What drivers reported
165/70R15 carries 2 complaints. Nobody has filed one naming 155/75R15.