185/60R15 vs 165/70R15
Going from one to the other changes the overall height by +1.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/60R15 | 165/70R15 | Change |
|---|---|---|---|
| Overall height | 23.7" | 24.1" | +1.5 % |
| Sidewall | 4.37" | 4.55" | +4.1 % |
| Section width | 185 mm | 165 mm | -10.8 % |
| Circumference | 74.6" | 75.7" | +1.5 % |
| Revs per mile | 850 | 837 | -1.5 % |
| Axle height | 11.87" | 12.05" | +4.5 mm |
| Approved rim width | 5–6.5" | 4.5–6" | overlap 5–6" |
Both are approved on a rim 5" to 6" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 185/60R15. Fit 165/70R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.3 mph | +1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,149 on the road, so it under-counts by 149. At a true 70 mph the first turns 991 times a minute, the second 977.