265/45R21 vs 255/45R21
Going from one to the other changes the overall height by -1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/45R21 | 255/45R21 | Change |
|---|---|---|---|
| Overall height | 30.4" | 30.0" | -1.2 % |
| Sidewall | 4.69" | 4.52" | -3.8 % |
| Section width | 265 mm | 255 mm | -3.8 % |
| Circumference | 95.5" | 94.4" | -1.2 % |
| Revs per mile | 664 | 671 | +1.2 % |
| Axle height | 15.19" | 15.02" | -4.5 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 265/45R21. Fit 255/45R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,883 on the road, so it over-counts by 117. At a true 70 mph the first turns 774 times a minute, the second 783.
What drivers reported
265/45R21 carries 2 complaints. Nobody has filed one naming 255/45R21.