225/45R17 vs 205/50R17
Going from one to the other changes the overall height by +0.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/45R17 | 205/50R17 | Change |
|---|---|---|---|
| Overall height | 25.0" | 25.1" | +0.4 % |
| Sidewall | 3.99" | 4.04" | +1.2 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 78.5" | 78.8" | +0.4 % |
| Revs per mile | 808 | 804 | -0.4 % |
| Axle height | 12.49" | 12.54" | +1.3 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 205/50R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.1 mph | +0.1 |
| 50 mph | 50.2 mph | +0.2 |
| 70 mph | 70.3 mph | +0.3 |
| 90 mph | 90.4 mph | +0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,039 on the road, so it under-counts by 39. At a true 70 mph the first turns 942 times a minute, the second 939.