155/75R15 vs 175/70R15
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 | 155/75R15 | 175/70R15 | Change |
|---|---|---|---|
| Overall height | 24.2" | 24.6" | +2.0 % |
| Sidewall | 4.58" | 4.82" | +5.4 % |
| Section width | 155 mm | 175 mm | +12.9 % |
| Circumference | 75.9" | 77.4" | +2.0 % |
| Revs per mile | 835 | 818 | -2.0 % |
| Axle height | 12.08" | 12.32" | +6.3 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 155/75R15. Fit 175/70R15 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 10,204 on the road, so it under-counts by 204. At a true 70 mph the first turns 974 times a minute, the second 955.
What drivers reported
Nobody has filed a complaint naming 155/75R15. 175/70R15 carries 2.