255/30R16 vs 235/35R16
Going from one to the other changes the overall height by +2.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/30R16 | 235/35R16 | Change |
|---|---|---|---|
| Overall height | 22.0" | 22.5" | +2.1 % |
| Sidewall | 3.01" | 3.24" | +7.5 % |
| Section width | 255 mm | 235 mm | -7.8 % |
| Circumference | 69.2" | 70.6" | +2.1 % |
| Revs per mile | 916 | 897 | -2.1 % |
| Axle height | 11.01" | 11.24" | +5.8 mm |
| Approved rim width | 7–9.5" | 6.5–8.5" | 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 255/30R16. Fit 235/35R16 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.9 mph | +1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,206 on the road, so it under-counts by 206. At a true 70 mph the first turns 1068 times a minute, the second 1047.