265/55R20 vs 255/60R20
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/55R20 | 255/60R20 | Change |
|---|---|---|---|
| Overall height | 31.5" | 32.0" | +1.8 % |
| Sidewall | 5.74" | 6.02" | +5.0 % |
| Section width | 265 mm | 255 mm | -3.8 % |
| Circumference | 98.9" | 100.7" | +1.8 % |
| Revs per mile | 641 | 629 | -1.8 % |
| Axle height | 15.74" | 16.02" | +7.3 mm |
| Approved rim width | 7.5–9.5" | 7–9.5" | 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 265/55R20. Fit 255/60R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,181 on the road, so it under-counts by 181. At a true 70 mph the first turns 748 times a minute, the second 734.
What drivers reported
265/55R20 carries 2 complaints. Nobody has filed one naming 255/60R20.