245/75R24 vs 255/70R24
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 | 245/75R24 | 255/70R24 | Change |
|---|---|---|---|
| Overall height | 38.5" | 38.1" | -1.1 % |
| Sidewall | 7.23" | 7.03" | -2.9 % |
| Section width | 245 mm | 255 mm | +4.1 % |
| Circumference | 120.9" | 119.6" | -1.1 % |
| Revs per mile | 524 | 530 | +1.1 % |
| Axle height | 19.23" | 19.03" | -5.3 mm |
| Approved rim width | 7–9" | 7–9.5" | overlap 7–9" |
Both are approved on a rim 7" to 9" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 245/75R24. Fit 255/70R24 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 | 69.2 mph | -0.8 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,893 on the road, so it over-counts by 107. At a true 70 mph the first turns 612 times a minute, the second 618.