315/55R18 vs 335/55R18
Going from one to the other changes the overall height by +2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/55R18 | 335/55R18 | Change |
|---|---|---|---|
| Overall height | 31.6" | 32.5" | +2.7 % |
| Sidewall | 6.82" | 7.25" | +6.3 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 99.4" | 102.1" | +2.7 % |
| Revs per mile | 637 | 620 | -2.7 % |
| Axle height | 15.82" | 16.25" | +11.0 mm |
| Approved rim width | 8.5–11.5" | 9.5–12.5" | overlap 9.5–11.5" |
Both are approved on a rim 9.5" to 11.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 315/55R18. Fit 335/55R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 71.9 mph | +1.9 |
| 90 mph | 92.5 mph | +2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,274 on the road, so it under-counts by 274. At a true 70 mph the first turns 744 times a minute, the second 724.