205/85R20 vs 225/75R20
Going from one to the other changes the overall height by -1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/85R20 | 225/75R20 | Change |
|---|---|---|---|
| Overall height | 33.7" | 33.3" | -1.3 % |
| Sidewall | 6.86" | 6.64" | -3.2 % |
| Section width | 205 mm | 225 mm | +9.8 % |
| Circumference | 105.9" | 104.6" | -1.3 % |
| Revs per mile | 598 | 606 | +1.3 % |
| Axle height | 16.86" | 16.64" | -5.5 mm |
| Approved rim width | 5.5–7.5" | 6–8.5" | overlap 6–7.5" |
Both are approved on a rim 6" to 7.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 205/85R20. Fit 225/75R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.8 mph | -1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,872 on the road, so it over-counts by 128. At a true 70 mph the first turns 698 times a minute, the second 707.