135/80R13 vs 135/85R13
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 | 135/80R13 | 135/85R13 | Change |
|---|---|---|---|
| Overall height | 21.5" | 22.0" | +2.5 % |
| Sidewall | 4.25" | 4.52" | +6.3 % |
| Section width | 135 mm | 135 mm | 0.0 % |
| Circumference | 67.6" | 69.2" | +2.5 % |
| Revs per mile | 938 | 915 | -2.5 % |
| Axle height | 10.75" | 11.02" | +6.8 mm |
| Approved rim width | 3.5–5" | 3.5–5" | overlap 3.5–5" |
Both are approved on a rim 3.5" to 5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 135/80R13. Fit 135/85R13 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 10,247 on the road, so it under-counts by 247. At a true 70 mph the first turns 1094 times a minute, the second 1068.