255/45R18 vs 275/45R18
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/45R18 | 275/45R18 | Change |
|---|---|---|---|
| Overall height | 27.0" | 27.7" | +2.6 % |
| Sidewall | 4.52" | 4.87" | +7.8 % |
| Section width | 255 mm | 275 mm | +7.8 % |
| Circumference | 84.9" | 87.2" | +2.6 % |
| Revs per mile | 746 | 727 | -2.6 % |
| Axle height | 13.52" | 13.87" | +9.0 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 255/45R18. Fit 275/45R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,262 on the road, so it under-counts by 262. At a true 70 mph the first turns 870 times a minute, the second 848.
What drivers reported
255/45R18 carries 6 complaints. Nobody has filed one naming 275/45R18.