225/60R15 vs 205/65R15
Going from one to the other changes the overall height by -0.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/60R15 | 205/65R15 | Change |
|---|---|---|---|
| Overall height | 25.6" | 25.5" | -0.5 % |
| Sidewall | 5.31" | 5.25" | -1.3 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 80.5" | 80.1" | -0.5 % |
| Revs per mile | 787 | 791 | +0.5 % |
| Axle height | 12.81" | 12.75" | -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 225/60R15. Fit 205/65R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.7 mph | -0.3 |
| 70 mph | 69.6 mph | -0.4 |
| 90 mph | 89.5 mph | -0.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,946 on the road, so it over-counts by 54. At a true 70 mph the first turns 918 times a minute, the second 923.