265/65R23 vs 245/75R23
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 | 265/65R23 | 245/75R23 | Change |
|---|---|---|---|
| Overall height | 36.6" | 37.5" | +2.5 % |
| Sidewall | 6.78" | 7.23" | +6.7 % |
| Section width | 265 mm | 245 mm | -7.5 % |
| Circumference | 114.9" | 117.7" | +2.5 % |
| Revs per mile | 552 | 538 | -2.5 % |
| Axle height | 18.28" | 18.73" | +11.5 mm |
| Approved rim width | 7.5–9.5" | 7–9" | overlap 7.5–9" |
Both are approved on a rim 7.5" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 265/65R23. Fit 245/75R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.7 mph | +1.7 |
| 90 mph | 92.2 mph | +2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,248 on the road, so it under-counts by 248. At a true 70 mph the first turns 644 times a minute, the second 628.