315/65R21 vs 335/65R21
Going from one to the other changes the overall height by +2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/65R21 | 335/65R21 | Change |
|---|---|---|---|
| Overall height | 37.1" | 38.1" | +2.8 % |
| Sidewall | 8.06" | 8.57" | +6.3 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 116.6" | 119.8" | +2.8 % |
| Revs per mile | 543 | 529 | -2.8 % |
| Axle height | 18.56" | 19.07" | +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 315/65R21. Fit 335/65R21 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 10,276 on the road, so it under-counts by 276. At a true 70 mph the first turns 634 times a minute, the second 617.