335/55R18 vs 355/50R18
Going from one to the other changes the overall height by -1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/55R18 | 355/50R18 | Change |
|---|---|---|---|
| Overall height | 32.5" | 32.0" | -1.6 % |
| Sidewall | 7.25" | 6.99" | -3.7 % |
| Section width | 335 mm | 355 mm | +6.0 % |
| Circumference | 102.1" | 100.5" | -1.6 % |
| Revs per mile | 620 | 631 | +1.6 % |
| Axle height | 16.25" | 15.99" | -6.8 mm |
| Approved rim width | 9.5–12.5" | 10–13" | overlap 10–12.5" |
Both are approved on a rim 10" 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 355/50R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.5 mph | -0.5 |
| 50 mph | 49.2 mph | -0.8 |
| 70 mph | 68.9 mph | -1.1 |
| 90 mph | 88.5 mph | -1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,837 on the road, so it over-counts by 163. At a true 70 mph the first turns 724 times a minute, the second 736.