255/40R23 vs 265/35R23
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/40R23 | 265/35R23 | Change |
|---|---|---|---|
| Overall height | 31.0" | 30.3" | -2.3 % |
| Sidewall | 4.02" | 3.65" | -9.1 % |
| Section width | 255 mm | 265 mm | +3.9 % |
| Circumference | 97.5" | 95.2" | -2.3 % |
| Revs per mile | 650 | 666 | +2.3 % |
| Axle height | 15.52" | 15.15" | -9.3 mm |
| Approved rim width | 7–9.5" | 7.5–9.5" | 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 255/40R23. Fit 265/35R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 87.9 mph | -2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,765 on the road, so it over-counts by 235. At a true 70 mph the first turns 758 times a minute, the second 776.