265/50R18 vs 275/50R18
Going from one to the other changes the overall height by +1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 265/50R18 | 275/50R18 | Change |
|---|---|---|---|
| Overall height | 28.4" | 28.8" | +1.4 % |
| Sidewall | 5.22" | 5.41" | +3.8 % |
| Section width | 265 mm | 275 mm | +3.8 % |
| Circumference | 89.3" | 90.6" | +1.4 % |
| Revs per mile | 709 | 700 | -1.4 % |
| Axle height | 14.22" | 14.41" | +5.0 mm |
| Approved rim width | 7.5–9.5" | 7.5–10" | overlap 7.5–9.5" |
Both are approved on a rim 7.5" 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 265/50R18. Fit 275/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.7 mph | +0.7 |
| 70 mph | 71.0 mph | +1.0 |
| 90 mph | 91.2 mph | +1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,138 on the road, so it under-counts by 138. At a true 70 mph the first turns 828 times a minute, the second 816.