225/80R19.5 vs 245/75R19.5
Going from one to the other changes the overall height by +0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/80R19.5 | 245/75R19.5 | Change |
|---|---|---|---|
| Overall height | 33.7" | 34.0" | +0.9 % |
| Sidewall | 7.09" | 7.23" | +2.1 % |
| Section width | 225 mm | 245 mm | +8.9 % |
| Circumference | 105.8" | 106.7" | +0.9 % |
| Revs per mile | 599 | 594 | -0.9 % |
| Axle height | 16.84" | 16.98" | +3.8 mm |
| Approved rim width | 6–8.5" | 7–9" | overlap 7–8.5" |
Both are approved on a rim 7" to 8.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 225/80R19.5. Fit 245/75R19.5 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.8 mph | +0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,088 on the road, so it under-counts by 88. At a true 70 mph the first turns 699 times a minute, the second 693.