215/60R20 vs 215/55R20
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 | 215/60R20 | 215/55R20 | Change |
|---|---|---|---|
| Overall height | 30.2" | 29.3" | -2.8 % |
| Sidewall | 5.08" | 4.66" | -8.3 % |
| Section width | 215 mm | 215 mm | 0.0 % |
| Circumference | 94.7" | 92.1" | -2.8 % |
| Revs per mile | 669 | 688 | +2.8 % |
| Axle height | 15.08" | 14.66" | -10.8 mm |
| Approved rim width | 6–8" | 6–8" | overlap 6–8" |
Both are approved on a rim 6" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 215/60R20. Fit 215/55R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,719 on the road, so it over-counts by 281. At a true 70 mph the first turns 780 times a minute, the second 803.