275/70R23 vs 275/75R23
Going from one to the other changes the overall height by +2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 275/70R23 | 275/75R23 | Change |
|---|---|---|---|
| Overall height | 38.2" | 39.2" | +2.8 % |
| Sidewall | 7.58" | 8.12" | +7.1 % |
| Section width | 275 mm | 275 mm | 0.0 % |
| Circumference | 119.9" | 123.3" | +2.8 % |
| Revs per mile | 529 | 514 | -2.8 % |
| Axle height | 19.08" | 19.62" | +13.8 mm |
| Approved rim width | 7.5–10" | 7.5–10" | overlap 7.5–10" |
Both are approved on a rim 7.5" to 10" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 275/70R23. Fit 275/75R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,284 on the road, so it under-counts by 284. At a true 70 mph the first turns 617 times a minute, the second 600.