205/55R20 vs 205/60R20
Going from one to the other changes the overall height by +2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/55R20 | 205/60R20 | Change |
|---|---|---|---|
| Overall height | 28.9" | 29.7" | +2.8 % |
| Sidewall | 4.44" | 4.84" | +9.1 % |
| Section width | 205 mm | 205 mm | 0.0 % |
| Circumference | 90.7" | 93.3" | +2.8 % |
| Revs per mile | 698 | 679 | -2.8 % |
| Axle height | 14.44" | 14.84" | +10.3 mm |
| Approved rim width | 5.5–7.5" | 5.5–7.5" | overlap 5.5–7.5" |
Both are approved on a rim 5.5" to 7.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 205/55R20. Fit 205/60R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.5 mph | +2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,279 on the road, so it under-counts by 279. At a true 70 mph the first turns 815 times a minute, the second 793.