315/35R21 vs 335/30R21
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 | 315/35R21 | 335/30R21 | Change |
|---|---|---|---|
| Overall height | 29.7" | 28.9" | -2.6 % |
| Sidewall | 4.34" | 3.96" | -8.8 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 93.2" | 90.8" | -2.6 % |
| Revs per mile | 679 | 698 | +2.6 % |
| Axle height | 14.84" | 14.46" | -9.8 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 315/35R21. Fit 335/30R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.7 mph | -1.3 |
| 70 mph | 68.2 mph | -1.8 |
| 90 mph | 87.7 mph | -2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,741 on the road, so it over-counts by 259. At a true 70 mph the first turns 793 times a minute, the second 814.