255/40R16 vs 275/40R16
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 | 255/40R16 | 275/40R16 | Change |
|---|---|---|---|
| Overall height | 24.0" | 24.7" | +2.6 % |
| Sidewall | 4.02" | 4.33" | +7.8 % |
| Section width | 255 mm | 275 mm | +7.8 % |
| Circumference | 75.5" | 77.5" | +2.6 % |
| Revs per mile | 839 | 818 | -2.6 % |
| Axle height | 12.02" | 12.33" | +8.0 mm |
| Approved rim width | 7–9.5" | 7.5–10" | 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 255/40R16. Fit 275/40R16 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 10,262 on the road, so it under-counts by 262. At a true 70 mph the first turns 979 times a minute, the second 954.