275/30R16 vs 255/35R16
Going from one to the other changes the overall height by +2.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/30R16 | 255/35R16 | Change |
|---|---|---|---|
| Overall height | 22.5" | 23.0" | +2.4 % |
| Sidewall | 3.25" | 3.51" | +8.2 % |
| Section width | 275 mm | 255 mm | -7.3 % |
| Circumference | 70.7" | 72.3" | +2.4 % |
| Revs per mile | 897 | 876 | -2.4 % |
| Axle height | 11.25" | 11.51" | +6.8 mm |
| Approved rim width | 7.5–10" | 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 275/30R16. Fit 255/35R16 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 | 92.1 mph | +2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,236 on the road, so it under-counts by 236. At a true 70 mph the first turns 1046 times a minute, the second 1022.