335/45R18 vs 355/40R18
Going from one to the other changes the overall height by -2.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/45R18 | 355/40R18 | Change |
|---|---|---|---|
| Overall height | 29.9" | 29.2" | -2.3 % |
| Sidewall | 5.94" | 5.59" | -5.8 % |
| Section width | 335 mm | 355 mm | +6.0 % |
| Circumference | 93.8" | 91.7" | -2.3 % |
| Revs per mile | 675 | 691 | +2.3 % |
| Axle height | 14.94" | 14.59" | -8.8 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 335/45R18. Fit 355/40R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 87.9 mph | -2.1 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,769 on the road, so it over-counts by 231. At a true 70 mph the first turns 788 times a minute, the second 806.