245/50R18 vs 265/50R18
Going from one to the other changes the overall height by +2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/50R18 | 265/50R18 | Change |
|---|---|---|---|
| Overall height | 27.6" | 28.4" | +2.8 % |
| Sidewall | 4.82" | 5.22" | +8.2 % |
| Section width | 245 mm | 265 mm | +8.2 % |
| Circumference | 86.9" | 89.3" | +2.8 % |
| Revs per mile | 730 | 709 | -2.8 % |
| Axle height | 13.82" | 14.22" | +10.0 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 265/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,285 on the road, so it under-counts by 285. At a true 70 mph the first turns 851 times a minute, the second 828.