225/85R15 vs 245/80R15
Going from one to the other changes the overall height by +1.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/85R15 | 245/80R15 | Change |
|---|---|---|---|
| Overall height | 30.1" | 30.4" | +1.2 % |
| Sidewall | 7.53" | 7.72" | +2.5 % |
| Section width | 225 mm | 245 mm | +8.9 % |
| Circumference | 94.4" | 95.6" | +1.2 % |
| Revs per mile | 671 | 663 | -1.2 % |
| Axle height | 15.03" | 15.22" | +4.8 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 225/85R15. Fit 245/80R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.4 mph | +0.4 |
| 50 mph | 50.6 mph | +0.6 |
| 70 mph | 70.9 mph | +0.9 |
| 90 mph | 91.1 mph | +1.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,124 on the road, so it under-counts by 124. At a true 70 mph the first turns 783 times a minute, the second 773.