275/55R21 vs 295/55R21
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/55R21 | 295/55R21 | Change |
|---|---|---|---|
| Overall height | 32.9" | 33.8" | +2.6 % |
| Sidewall | 5.95" | 6.39" | +7.3 % |
| Section width | 275 mm | 295 mm | +7.3 % |
| Circumference | 103.4" | 106.1" | +2.6 % |
| Revs per mile | 613 | 597 | -2.6 % |
| Axle height | 16.45" | 16.89" | +11.0 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 275/55R21. Fit 295/55R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,263 on the road, so it under-counts by 263. At a true 70 mph the first turns 715 times a minute, the second 697.