225/60R20 vs 205/65R20
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 | 225/60R20 | 205/65R20 | Change |
|---|---|---|---|
| Overall height | 30.6" | 30.5" | -0.4 % |
| Sidewall | 5.31" | 5.25" | -1.3 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 96.2" | 95.8" | -0.4 % |
| Revs per mile | 658 | 661 | +0.4 % |
| Axle height | 15.31" | 15.25" | -1.8 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 225/60R20. Fit 205/65R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.9 mph | -0.1 |
| 50 mph | 49.8 mph | -0.2 |
| 70 mph | 69.7 mph | -0.3 |
| 90 mph | 89.6 mph | -0.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,955 on the road, so it over-counts by 45. At a true 70 mph the first turns 768 times a minute, the second 772.