225/85R15 vs 225/80R15
Going from one to the other changes the overall height by -2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/85R15 | 225/80R15 | Change |
|---|---|---|---|
| Overall height | 30.1" | 29.2" | -2.9 % |
| Sidewall | 7.53" | 7.09" | -5.9 % |
| Section width | 225 mm | 225 mm | 0.0 % |
| Circumference | 94.4" | 91.7" | -2.9 % |
| Revs per mile | 671 | 691 | +2.9 % |
| Axle height | 15.03" | 14.59" | -11.3 mm |
| Approved rim width | 6–8.5" | 6–8.5" | overlap 6–8.5" |
Both are approved on a rim 6" 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 225/80R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.5 mph | -1.5 |
| 70 mph | 67.9 mph | -2.1 |
| 90 mph | 87.3 mph | -2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,705 on the road, so it over-counts by 295. At a true 70 mph the first turns 783 times a minute, the second 807.