265/45R21 vs 255/50R21
Going from one to the other changes the overall height by +2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/45R21 | 255/50R21 | Change |
|---|---|---|---|
| Overall height | 30.4" | 31.0" | +2.1 % |
| Sidewall | 4.69" | 5.02" | +6.9 % |
| Section width | 265 mm | 255 mm | -3.8 % |
| Circumference | 95.5" | 97.5" | +2.1 % |
| Revs per mile | 664 | 650 | -2.1 % |
| Axle height | 15.19" | 15.52" | +8.3 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 265/45R21. Fit 255/50R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 91.9 mph | +1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,214 on the road, so it under-counts by 214. At a true 70 mph the first turns 774 times a minute, the second 758.
What drivers reported
265/45R21 carries 2 complaints. Nobody has filed one naming 255/50R21.