225/40R20 vs 215/45R20
Going from one to the other changes the overall height by +2.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/40R20 | 215/45R20 | Change |
|---|---|---|---|
| Overall height | 27.1" | 27.6" | +2.0 % |
| Sidewall | 3.54" | 3.81" | +7.5 % |
| Section width | 225 mm | 215 mm | -4.4 % |
| Circumference | 85.1" | 86.8" | +2.0 % |
| Revs per mile | 745 | 730 | -2.0 % |
| Axle height | 13.54" | 13.81" | +6.8 mm |
| Approved rim width | 6–8.5" | 6–8" | overlap 6–8" |
Both are approved on a rim 6" to 8" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 225/40R20. Fit 215/45R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 51.0 mph | +1.0 |
| 70 mph | 71.4 mph | +1.4 |
| 90 mph | 91.8 mph | +1.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,196 on the road, so it under-counts by 196. At a true 70 mph the first turns 869 times a minute, the second 852.