255/60R20 vs 275/55R20
Going from one to the other changes the overall height by -0.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/60R20 | 275/55R20 | Change |
|---|---|---|---|
| Overall height | 32.0" | 31.9" | -0.4 % |
| Sidewall | 6.02" | 5.95" | -1.1 % |
| Section width | 255 mm | 275 mm | +7.8 % |
| Circumference | 100.7" | 100.2" | -0.4 % |
| Revs per mile | 629 | 632 | +0.4 % |
| Axle height | 16.02" | 15.95" | -1.8 mm |
| Approved rim width | 7–9.5" | 7.5–10" | overlap 7.5–9.5" |
Both are approved on a rim 7.5" to 9.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 255/60R20. Fit 275/55R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.8 mph | -0.2 |
| 70 mph | 69.7 mph | -0.3 |
| 90 mph | 89.6 mph | -0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,957 on the road, so it over-counts by 43. At a true 70 mph the first turns 734 times a minute, the second 737.
What drivers reported
Nobody has filed a complaint naming 255/60R20. 275/55R20 carries 55.