235/35R16 vs 255/35R16
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 | 235/35R16 | 255/35R16 | Change |
|---|---|---|---|
| Overall height | 22.5" | 23.0" | +2.5 % |
| Sidewall | 3.24" | 3.51" | +8.5 % |
| Section width | 235 mm | 255 mm | +8.5 % |
| Circumference | 70.6" | 72.3" | +2.5 % |
| Revs per mile | 897 | 876 | -2.5 % |
| Axle height | 11.24" | 11.51" | +7.0 mm |
| Approved rim width | 6.5–8.5" | 7–9.5" | overlap 7–8.5" |
Both are approved on a rim 7" to 8.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 235/35R16. 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 | 92.2 mph | +2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,245 on the road, so it under-counts by 245. At a true 70 mph the first turns 1047 times a minute, the second 1022.