225/40R15 vs 205/45R15
Going from one to the other changes the overall height by +0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/40R15 | 205/45R15 | Change |
|---|---|---|---|
| Overall height | 22.1" | 22.3" | +0.8 % |
| Sidewall | 3.54" | 3.63" | +2.5 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 69.4" | 69.9" | +0.8 % |
| Revs per mile | 913 | 906 | -0.8 % |
| Axle height | 11.04" | 11.13" | +2.3 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 225/40R15. Fit 205/45R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.7 mph | +0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,080 on the road, so it under-counts by 80. At a true 70 mph the first turns 1065 times a minute, the second 1057.
What drivers reported
Nobody has filed a complaint naming 225/40R15. 205/45R15 carries 2.