355/50R18 vs 335/55R18
Going from one to the other changes the overall height by +1.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 355/50R18 | 335/55R18 | Change |
|---|---|---|---|
| Overall height | 32.0" | 32.5" | +1.7 % |
| Sidewall | 6.99" | 7.25" | +3.8 % |
| Section width | 355 mm | 335 mm | -5.6 % |
| Circumference | 100.5" | 102.1" | +1.7 % |
| Revs per mile | 631 | 620 | -1.7 % |
| Axle height | 15.99" | 16.25" | +6.8 mm |
| Approved rim width | 10–13" | 9.5–12.5" | 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 355/50R18. Fit 335/55R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.2 mph | +1.2 |
| 90 mph | 91.5 mph | +1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,166 on the road, so it under-counts by 166. At a true 70 mph the first turns 736 times a minute, the second 724.