225/60R15 vs 205/70R15
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/60R15 | 205/70R15 | Change |
|---|---|---|---|
| Overall height | 25.6" | 26.3" | +2.6 % |
| Sidewall | 5.31" | 5.65" | +6.3 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 80.5" | 82.6" | +2.6 % |
| Revs per mile | 787 | 767 | -2.6 % |
| Axle height | 12.81" | 13.15" | +8.5 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 205/70R15 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,261 on the road, so it under-counts by 261. At a true 70 mph the first turns 918 times a minute, the second 895.