215/70R18 vs 225/65R18
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 215/70R18 | 225/65R18 | Change |
|---|---|---|---|
| Overall height | 29.9" | 29.5" | -1.1 % |
| Sidewall | 5.93" | 5.76" | -2.8 % |
| Section width | 215 mm | 225 mm | +4.7 % |
| Circumference | 93.8" | 92.7" | -1.1 % |
| Revs per mile | 676 | 683 | +1.1 % |
| Axle height | 14.93" | 14.76" | -4.3 mm |
| Approved rim width | 6–8" | 6–8.5" | 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 215/70R18. Fit 225/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.4 mph | -0.6 |
| 70 mph | 69.2 mph | -0.8 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,888 on the road, so it over-counts by 112. At a true 70 mph the first turns 788 times a minute, the second 797.