315/45R21 vs 335/45R21
Going from one to the other changes the overall height by +2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/45R21 | 335/45R21 | Change |
|---|---|---|---|
| Overall height | 32.2" | 32.9" | +2.2 % |
| Sidewall | 5.58" | 5.94" | +6.3 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 101.0" | 103.3" | +2.2 % |
| Revs per mile | 627 | 614 | -2.2 % |
| Axle height | 16.08" | 16.44" | +9.0 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 315/45R21. Fit 335/45R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 92.0 mph | +2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,220 on the road, so it under-counts by 220. At a true 70 mph the first turns 732 times a minute, the second 716.