275/40R23 vs 285/35R23
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 | 275/40R23 | 285/35R23 | Change |
|---|---|---|---|
| Overall height | 31.7" | 30.9" | -2.5 % |
| Sidewall | 4.33" | 3.93" | -9.3 % |
| Section width | 275 mm | 285 mm | +3.6 % |
| Circumference | 99.5" | 96.9" | -2.5 % |
| Revs per mile | 637 | 654 | +2.5 % |
| Axle height | 15.83" | 15.43" | -10.3 mm |
| Approved rim width | 7.5–10" | 8–10.5" | overlap 8–10" |
Both are approved on a rim 8" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/40R23. Fit 285/35R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,745 on the road, so it over-counts by 255. At a true 70 mph the first turns 743 times a minute, the second 763.