285/45R18 vs 265/50R18
Going from one to the other changes the overall height by +1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 285/45R18 | 265/50R18 | Change |
|---|---|---|---|
| Overall height | 28.1" | 28.4" | +1.2 % |
| Sidewall | 5.05" | 5.22" | +3.3 % |
| Section width | 285 mm | 265 mm | -7.0 % |
| Circumference | 88.3" | 89.3" | +1.2 % |
| Revs per mile | 718 | 709 | -1.2 % |
| Axle height | 14.05" | 14.22" | +4.3 mm |
| Approved rim width | 8–10.5" | 7.5–9.5" | overlap 8–9.5" |
Both are approved on a rim 8" 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 285/45R18. Fit 265/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.8 mph | +0.8 |
| 90 mph | 91.1 mph | +1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,119 on the road, so it under-counts by 119. At a true 70 mph the first turns 837 times a minute, the second 828.