315/30R18 vs 335/30R18
Going from one to the other changes the overall height by +1.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/30R18 | 335/30R18 | Change |
|---|---|---|---|
| Overall height | 25.4" | 25.9" | +1.9 % |
| Sidewall | 3.72" | 3.96" | +6.3 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 79.9" | 81.4" | +1.9 % |
| Revs per mile | 793 | 778 | -1.9 % |
| Axle height | 12.72" | 12.96" | +6.0 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 315/30R18. Fit 335/30R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.6 mph | +0.6 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.7 mph | +1.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,186 on the road, so it under-counts by 186. At a true 70 mph the first turns 925 times a minute, the second 908.