195/45R17 vs 205/40R17
Going from one to the other changes the overall height by -1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/45R17 | 205/40R17 | Change |
|---|---|---|---|
| Overall height | 23.9" | 23.5" | -1.9 % |
| Sidewall | 3.45" | 3.23" | -6.6 % |
| Section width | 195 mm | 205 mm | +5.1 % |
| Circumference | 75.1" | 73.7" | -1.9 % |
| Revs per mile | 844 | 860 | +1.9 % |
| Axle height | 11.95" | 11.73" | -5.8 mm |
| Approved rim width | 5.5–7" | 5.5–7.5" | overlap 5.5–7" |
Both are approved on a rim 5.5" to 7" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 195/45R17. Fit 205/40R17 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.4 mph | -0.6 |
| 50 mph | 49.1 mph | -0.9 |
| 70 mph | 68.7 mph | -1.3 |
| 90 mph | 88.3 mph | -1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,811 on the road, so it over-counts by 189. At a true 70 mph the first turns 984 times a minute, the second 1003.