285/45R23 vs 295/40R23
Going from one to the other changes the overall height by -2.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/45R23 | 295/40R23 | Change |
|---|---|---|---|
| Overall height | 33.1" | 32.3" | -2.4 % |
| Sidewall | 5.05" | 4.65" | -8.0 % |
| Section width | 285 mm | 295 mm | +3.5 % |
| Circumference | 104.0" | 101.4" | -2.4 % |
| Revs per mile | 609 | 625 | +2.4 % |
| Axle height | 16.55" | 16.15" | -10.3 mm |
| Approved rim width | 8–10.5" | 8.5–11" | overlap 8.5–10.5" |
Both are approved on a rim 8.5" to 10.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 285/45R23. Fit 295/40R23 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 | 68.3 mph | -1.7 |
| 90 mph | 87.8 mph | -2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,756 on the road, so it over-counts by 244. At a true 70 mph the first turns 711 times a minute, the second 729.