345/65R18 vs 335/65R18
Going from one to the other changes the overall height by -1.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/65R18 | 335/65R18 | Change |
|---|---|---|---|
| Overall height | 35.7" | 35.1" | -1.4 % |
| Sidewall | 8.83" | 8.57" | -2.9 % |
| Section width | 345 mm | 335 mm | -2.9 % |
| Circumference | 112.0" | 110.4" | -1.4 % |
| Revs per mile | 566 | 574 | +1.4 % |
| Axle height | 17.83" | 17.57" | -6.5 mm |
| Approved rim width | 9.5–12.5" | 9.5–12.5" | overlap 9.5–12.5" |
Both are approved on a rim 9.5" to 12.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 345/65R18. Fit 335/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.0 mph | -1.0 |
| 90 mph | 88.7 mph | -1.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,856 on the road, so it over-counts by 144. At a true 70 mph the first turns 660 times a minute, the second 669.