225/50R20 vs 205/50R20
Going from one to the other changes the overall height by -2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/50R20 | 205/50R20 | Change |
|---|---|---|---|
| Overall height | 28.9" | 28.1" | -2.7 % |
| Sidewall | 4.43" | 4.04" | -8.9 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 90.7" | 88.2" | -2.7 % |
| Revs per mile | 699 | 718 | +2.7 % |
| Axle height | 14.43" | 14.04" | -10.0 mm |
| Approved rim width | 6–8.5" | 5.5–7.5" | 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 225/50R20. Fit 205/50R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.1 mph | -1.9 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,727 on the road, so it over-counts by 273. At a true 70 mph the first turns 815 times a minute, the second 838.