245/45R23 vs 265/40R23
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 245/45R23 | 265/40R23 | Change |
|---|---|---|---|
| Overall height | 31.7" | 31.3" | -1.1 % |
| Sidewall | 4.34" | 4.17" | -3.9 % |
| Section width | 245 mm | 265 mm | +8.2 % |
| Circumference | 99.5" | 98.5" | -1.1 % |
| Revs per mile | 637 | 643 | +1.1 % |
| Axle height | 15.84" | 15.67" | -4.3 mm |
| Approved rim width | 7–9" | 7.5–9.5" | 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 245/45R23. Fit 265/40R23 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.3 mph | -0.7 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,894 on the road, so it over-counts by 106. At a true 70 mph the first turns 743 times a minute, the second 751.