335/55R18 vs 345/50R18
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/55R18 | 345/50R18 | Change |
|---|---|---|---|
| Overall height | 32.5" | 31.6" | -2.8 % |
| Sidewall | 7.25" | 6.79" | -6.4 % |
| Section width | 335 mm | 345 mm | +3.0 % |
| Circumference | 102.1" | 99.2" | -2.8 % |
| Revs per mile | 620 | 639 | +2.8 % |
| Axle height | 16.25" | 15.79" | -11.8 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 335/55R18. Fit 345/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.1 mph | -0.9 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.4 mph | -2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,715 on the road, so it over-counts by 285. At a true 70 mph the first turns 724 times a minute, the second 745.