275/50R21 vs 295/50R21
Going from one to the other changes the overall height by +2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/50R21 | 295/50R21 | Change |
|---|---|---|---|
| Overall height | 31.8" | 32.6" | +2.5 % |
| Sidewall | 5.41" | 5.81" | +7.3 % |
| Section width | 275 mm | 295 mm | +7.3 % |
| Circumference | 100.0" | 102.5" | +2.5 % |
| Revs per mile | 634 | 618 | -2.5 % |
| Axle height | 15.91" | 16.31" | +10.0 mm |
| Approved rim width | 7.5–10" | 8.5–11" | overlap 8.5–10" |
Both are approved on a rim 8.5" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/50R21. Fit 295/50R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.7 mph | +1.7 |
| 90 mph | 92.2 mph | +2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,247 on the road, so it under-counts by 247. At a true 70 mph the first turns 739 times a minute, the second 721.