245/50R18 vs 265/45R18
Going from one to the other changes the overall height by -0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/50R18 | 265/45R18 | Change |
|---|---|---|---|
| Overall height | 27.6" | 27.4" | -0.9 % |
| Sidewall | 4.82" | 4.69" | -2.7 % |
| Section width | 245 mm | 265 mm | +8.2 % |
| Circumference | 86.9" | 86.0" | -0.9 % |
| Revs per mile | 730 | 736 | +0.9 % |
| Axle height | 13.82" | 13.69" | -3.3 mm |
| Approved rim width | 7–9" | 7.5–9.5" | overlap 7.5–9" |
Both are approved on a rim 7.5" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 245/50R18. Fit 265/45R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.4 mph | -0.6 |
| 90 mph | 89.2 mph | -0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,907 on the road, so it over-counts by 93. At a true 70 mph the first turns 851 times a minute, the second 859.