245/75R22.5 vs 255/70R22.5
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 | 245/75R22.5 | 255/70R22.5 | Change |
|---|---|---|---|
| Overall height | 37.0" | 36.6" | -1.1 % |
| Sidewall | 7.23" | 7.03" | -2.9 % |
| Section width | 245 mm | 255 mm | +4.1 % |
| Circumference | 116.1" | 114.8" | -1.1 % |
| Revs per mile | 546 | 552 | +1.1 % |
| Axle height | 18.48" | 18.28" | -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 245/75R22.5. Fit 255/70R22.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.4 mph | -0.6 |
| 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 9,888 on the road, so it over-counts by 112. At a true 70 mph the first turns 636 times a minute, the second 644.
What drivers reported
Nobody has filed a complaint naming 245/75R22.5. 255/70R22.5 carries 7 and 2 deaths.