175/65R15 vs 155/70R15
Going from one to the other changes the overall height by -1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 175/65R15 | 155/70R15 | Change |
|---|---|---|---|
| Overall height | 24.0" | 23.5" | -1.7 % |
| Sidewall | 4.48" | 4.27" | -4.6 % |
| Section width | 175 mm | 155 mm | -11.4 % |
| Circumference | 75.3" | 74.0" | -1.7 % |
| Revs per mile | 842 | 857 | +1.7 % |
| Axle height | 11.98" | 11.77" | -5.3 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 175/65R15. Fit 155/70R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.8 mph | -1.2 |
| 90 mph | 88.4 mph | -1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,827 on the road, so it over-counts by 173. At a true 70 mph the first turns 982 times a minute, the second 999.
What drivers reported
175/65R15 carries 6 complaints. Nobody has filed one naming 155/70R15.