265/70R18 vs 255/75R18
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 | 265/70R18 | 255/75R18 | Change |
|---|---|---|---|
| Overall height | 32.6" | 33.1" | +1.4 % |
| Sidewall | 7.30" | 7.53" | +3.1 % |
| Section width | 265 mm | 255 mm | -3.8 % |
| Circumference | 102.4" | 103.9" | +1.4 % |
| Revs per mile | 619 | 610 | -1.4 % |
| Axle height | 16.30" | 16.53" | +5.8 mm |
| Approved rim width | 7.5–9.5" | 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 265/70R18. Fit 255/75R18 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 10,139 on the road, so it under-counts by 139. At a true 70 mph the first turns 722 times a minute, the second 712.
What drivers reported
265/70R18 carries 20 complaints. Nobody has filed one naming 255/75R18.