225/55R18 vs 205/65R18
Going from one to the other changes the overall height by +2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 225/55R18 | 205/65R18 | Change |
|---|---|---|---|
| Overall height | 27.7" | 28.5" | +2.7 % |
| Sidewall | 4.87" | 5.25" | +7.7 % |
| Section width | 225 mm | 205 mm | -8.9 % |
| Circumference | 87.2" | 89.5" | +2.7 % |
| Revs per mile | 727 | 708 | -2.7 % |
| Axle height | 13.87" | 14.25" | +9.5 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 225/55R18. Fit 205/65R18 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 | 71.9 mph | +1.9 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,270 on the road, so it under-counts by 270. At a true 70 mph the first turns 848 times a minute, the second 826.
What drivers reported
225/55R18 carries 11 complaints. Nobody has filed one naming 205/65R18.