255/35R19 vs 235/35R19
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 | 255/35R19 | 235/35R19 | Change |
|---|---|---|---|
| Overall height | 26.0" | 25.5" | -2.1 % |
| Sidewall | 3.51" | 3.24" | -7.8 % |
| Section width | 255 mm | 235 mm | -7.8 % |
| Circumference | 81.8" | 80.0" | -2.1 % |
| Revs per mile | 775 | 792 | +2.1 % |
| Axle height | 13.01" | 12.74" | -7.0 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 255/35R19. Fit 235/35R19 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.5 mph | -1.5 |
| 90 mph | 88.1 mph | -1.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,788 on the road, so it over-counts by 212. At a true 70 mph the first turns 904 times a minute, the second 924.