215/45R20 vs 205/50R20
Going from one to the other changes the overall height by +1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/45R20 | 205/50R20 | Change |
|---|---|---|---|
| Overall height | 27.6" | 28.1" | +1.6 % |
| Sidewall | 3.81" | 4.04" | +5.9 % |
| Section width | 215 mm | 205 mm | -4.7 % |
| Circumference | 86.8" | 88.2" | +1.6 % |
| Revs per mile | 730 | 718 | -1.6 % |
| Axle height | 13.81" | 14.04" | +5.8 mm |
| Approved rim width | 6–8" | 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 215/45R20. Fit 205/50R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.1 mph | +1.1 |
| 90 mph | 91.5 mph | +1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,164 on the road, so it under-counts by 164. At a true 70 mph the first turns 852 times a minute, the second 838.