155/75R13 vs 145/85R13
Going from one to the other changes the overall height by +2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 155/75R13 | 145/85R13 | Change |
|---|---|---|---|
| Overall height | 22.2" | 22.7" | +2.5 % |
| Sidewall | 4.58" | 4.85" | +6.0 % |
| Section width | 155 mm | 145 mm | -6.5 % |
| Circumference | 69.6" | 71.3" | +2.5 % |
| Revs per mile | 910 | 888 | -2.5 % |
| Axle height | 11.08" | 11.35" | +7.0 mm |
| Approved rim width | 4–5.5" | 4–5.5" | overlap 4–5.5" |
Both are approved on a rim 4" 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 155/75R13. Fit 145/85R13 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.7 mph | +1.7 |
| 90 mph | 92.2 mph | +2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,249 on the road, so it under-counts by 249. At a true 70 mph the first turns 1062 times a minute, the second 1036.