315/55R20 vs 335/55R20
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/55R20 | 335/55R20 | Change |
|---|---|---|---|
| Overall height | 33.6" | 34.5" | +2.6 % |
| Sidewall | 6.82" | 7.25" | +6.3 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 105.7" | 108.4" | +2.6 % |
| Revs per mile | 599 | 584 | -2.6 % |
| Axle height | 16.82" | 17.25" | +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 315/55R20. Fit 335/55R20 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,257 on the road, so it under-counts by 257. At a true 70 mph the first turns 699 times a minute, the second 682.