165/80R15 vs 185/75R15
Going from one to the other changes the overall height by +2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 165/80R15 | 185/75R15 | Change |
|---|---|---|---|
| Overall height | 25.4" | 25.9" | +2.1 % |
| Sidewall | 5.20" | 5.46" | +5.1 % |
| Section width | 165 mm | 185 mm | +12.1 % |
| Circumference | 79.8" | 81.4" | +2.1 % |
| Revs per mile | 794 | 778 | -2.1 % |
| Axle height | 12.70" | 12.96" | +6.8 mm |
| Approved rim width | 4.5–6" | 5–6.5" | 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 165/80R15. Fit 185/75R15 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 | 71.5 mph | +1.5 |
| 90 mph | 91.9 mph | +1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,209 on the road, so it under-counts by 209. At a true 70 mph the first turns 927 times a minute, the second 908.
What drivers reported
165/80R15 carries 4 complaints. Nobody has filed one naming 185/75R15.