185/75R18 vs 195/70R18
Going from one to the other changes the overall height by -0.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 185/75R18 | 195/70R18 | Change |
|---|---|---|---|
| Overall height | 28.9" | 28.7" | -0.6 % |
| Sidewall | 5.46" | 5.37" | -1.6 % |
| Section width | 185 mm | 195 mm | +5.4 % |
| Circumference | 90.9" | 90.3" | -0.6 % |
| Revs per mile | 697 | 702 | +0.6 % |
| Axle height | 14.46" | 14.37" | -2.3 mm |
| Approved rim width | 5–6.5" | 5.5–7" | overlap 5.5–6.5" |
Both are approved on a rim 5.5" to 6.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 185/75R18. Fit 195/70R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.7 mph | -0.3 |
| 70 mph | 69.6 mph | -0.4 |
| 90 mph | 89.4 mph | -0.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,939 on the road, so it over-counts by 61. At a true 70 mph the first turns 813 times a minute, the second 818.
What drivers reported
Nobody has filed a complaint naming 185/75R18. 195/70R18 carries 1.