315/65R18 vs 335/65R18
Going from one to the other changes the overall height by +3.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/65R18 | 335/65R18 | Change |
|---|---|---|---|
| Overall height | 34.1" | 35.1" | +3.0 % |
| Sidewall | 8.06" | 8.57" | +6.3 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 107.2" | 110.4" | +3.0 % |
| Revs per mile | 591 | 574 | -3.0 % |
| Axle height | 17.06" | 17.57" | +13.0 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 315/65R18. Fit 335/65R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.5 mph | +1.5 |
| 70 mph | 72.1 mph | +2.1 |
| 90 mph | 92.7 mph | +2.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,300 on the road, so it under-counts by 300. At a true 70 mph the first turns 690 times a minute, the second 669.