255/50R18 vs 275/45R18
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/50R18 | 275/45R18 | Change |
|---|---|---|---|
| Overall height | 28.0" | 27.7" | -1.1 % |
| Sidewall | 5.02" | 4.87" | -2.9 % |
| Section width | 255 mm | 275 mm | +7.8 % |
| Circumference | 88.1" | 87.2" | -1.1 % |
| Revs per mile | 719 | 727 | +1.1 % |
| Axle height | 14.02" | 13.87" | -3.8 mm |
| Approved rim width | 7–9.5" | 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 255/50R18. Fit 275/45R18 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 | 69.3 mph | -0.7 |
| 90 mph | 89.1 mph | -0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,895 on the road, so it over-counts by 105. At a true 70 mph the first turns 839 times a minute, the second 848.
What drivers reported
255/50R18 carries 1 complaints. Nobody has filed one naming 275/45R18.