265/30R23 vs 255/35R23
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/30R23 | 255/35R23 | Change |
|---|---|---|---|
| Overall height | 29.3" | 30.0" | +2.6 % |
| Sidewall | 3.13" | 3.51" | +12.3 % |
| Section width | 265 mm | 255 mm | -3.8 % |
| Circumference | 91.9" | 94.3" | +2.6 % |
| Revs per mile | 689 | 672 | -2.6 % |
| Axle height | 14.63" | 15.01" | +9.8 mm |
| Approved rim width | 7.5–9.5" | 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 265/30R23. Fit 255/35R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,262 on the road, so it under-counts by 262. At a true 70 mph the first turns 804 times a minute, the second 784.