205/70R18 vs 195/75R18
Going from one to the other changes the overall height by +0.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 205/70R18 | 195/75R18 | Change |
|---|---|---|---|
| Overall height | 29.3" | 29.5" | +0.7 % |
| Sidewall | 5.65" | 5.76" | +1.9 % |
| Section width | 205 mm | 195 mm | -4.9 % |
| Circumference | 92.0" | 92.7" | +0.7 % |
| Revs per mile | 688 | 683 | -0.7 % |
| Axle height | 14.65" | 14.76" | +2.8 mm |
| Approved rim width | 5.5–7.5" | 5.5–7" | 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 205/70R18. Fit 195/75R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.5 mph | +0.5 |
| 90 mph | 90.7 mph | +0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,074 on the road, so it under-counts by 74. At a true 70 mph the first turns 803 times a minute, the second 797.