275/55R23 vs 255/55R23
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/55R23 | 255/55R23 | Change |
|---|---|---|---|
| Overall height | 34.9" | 34.0" | -2.5 % |
| Sidewall | 5.95" | 5.52" | -7.3 % |
| Section width | 275 mm | 255 mm | -7.3 % |
| Circumference | 109.7" | 107.0" | -2.5 % |
| Revs per mile | 578 | 592 | +2.5 % |
| Axle height | 17.45" | 17.02" | -11.0 mm |
| Approved rim width | 7.5–10" | 7–9.5" | 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 275/55R23. Fit 255/55R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.3 mph | -1.7 |
| 90 mph | 87.8 mph | -2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,752 on the road, so it over-counts by 248. At a true 70 mph the first turns 674 times a minute, the second 691.