225/45R17 vs 205/45R17
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/45R17 | 205/45R17 | Change |
|---|---|---|---|
| Overall height | 25.0" | 24.3" | -2.8 % |
| Sidewall | 3.99" | 3.63" | -8.9 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 78.5" | 76.2" | -2.8 % |
| Revs per mile | 808 | 831 | +2.8 % |
| Axle height | 12.49" | 12.13" | -9.0 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 225/45R17. Fit 205/45R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.4 mph | -2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,716 on the road, so it over-counts by 284. At a true 70 mph the first turns 942 times a minute, the second 970.