275/35R15 vs 255/35R15
Going from one to the other changes the overall height by -2.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/35R15 | 255/35R15 | Change |
|---|---|---|---|
| Overall height | 22.6" | 22.0" | -2.4 % |
| Sidewall | 3.79" | 3.51" | -7.3 % |
| Section width | 275 mm | 255 mm | -7.3 % |
| Circumference | 70.9" | 69.2" | -2.4 % |
| Revs per mile | 893 | 916 | +2.4 % |
| Axle height | 11.29" | 11.01" | -7.0 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 275/35R15. Fit 255/35R15 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 9,756 on the road, so it over-counts by 244. At a true 70 mph the first turns 1042 times a minute, the second 1068.