255/70R23 vs 275/65R23
Going from one to the other changes the overall height by +0.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 255/70R23 | 275/65R23 | Change |
|---|---|---|---|
| Overall height | 37.1" | 37.1" | +0.1 % |
| Sidewall | 7.03" | 7.04" | +0.1 % |
| Section width | 255 mm | 275 mm | +7.8 % |
| Circumference | 116.4" | 116.5" | +0.1 % |
| Revs per mile | 544 | 544 | -0.1 % |
| Axle height | 18.53" | 18.54" | +0.3 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 255/70R23. Fit 275/65R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.0 mph | +0.0 |
| 50 mph | 50.0 mph | +0.0 |
| 70 mph | 70.0 mph | +0.0 |
| 90 mph | 90.0 mph | +0.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,005 on the road, so it under-counts by 5. At a true 70 mph the first turns 635 times a minute, the second 635.