195/65R18 vs 205/65R18
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 195/65R18 | 205/65R18 | Change |
|---|---|---|---|
| Overall height | 28.0" | 28.5" | +1.8 % |
| Sidewall | 4.99" | 5.25" | +5.1 % |
| Section width | 195 mm | 205 mm | +5.1 % |
| Circumference | 87.9" | 89.5" | +1.8 % |
| Revs per mile | 721 | 708 | -1.8 % |
| Axle height | 13.99" | 14.25" | +6.5 mm |
| Approved rim width | 5.5–7" | 5.5–7.5" | overlap 5.5–7" |
Both are approved on a rim 5.5" to 7" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 195/65R18. Fit 205/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,183 on the road, so it under-counts by 183. At a true 70 mph the first turns 841 times a minute, the second 826.