195/70R18 vs 185/75R18
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 | 195/70R18 | 185/75R18 | Change |
|---|---|---|---|
| Overall height | 28.7" | 28.9" | +0.6 % |
| Sidewall | 5.37" | 5.46" | +1.6 % |
| Section width | 195 mm | 185 mm | -5.1 % |
| Circumference | 90.3" | 90.9" | +0.6 % |
| Revs per mile | 702 | 697 | -0.6 % |
| Axle height | 14.37" | 14.46" | +2.3 mm |
| Approved rim width | 5.5–7" | 5–6.5" | 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 195/70R18. Fit 185/75R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.3 mph | +0.3 |
| 70 mph | 70.4 mph | +0.4 |
| 90 mph | 90.6 mph | +0.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,062 on the road, so it under-counts by 62. At a true 70 mph the first turns 818 times a minute, the second 813.
What drivers reported
195/70R18 carries 1 complaints. Nobody has filed one naming 185/75R18.