255/35R24 vs 275/35R24
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/35R24 | 275/35R24 | Change |
|---|---|---|---|
| Overall height | 31.0" | 31.6" | +1.8 % |
| Sidewall | 3.51" | 3.79" | +7.8 % |
| Section width | 255 mm | 275 mm | +7.8 % |
| Circumference | 97.5" | 99.2" | +1.8 % |
| Revs per mile | 650 | 639 | -1.8 % |
| Axle height | 15.51" | 15.79" | +7.0 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 255/35R24. Fit 275/35R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,178 on the road, so it under-counts by 178. At a true 70 mph the first turns 758 times a minute, the second 745.