315/55R21 vs 335/50R21
Going from one to the other changes the overall height by -1.3 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/55R21 | 335/50R21 | Change |
|---|---|---|---|
| Overall height | 34.6" | 34.2" | -1.3 % |
| Sidewall | 6.82" | 6.59" | -3.3 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 108.8" | 107.4" | -1.3 % |
| Revs per mile | 582 | 590 | +1.3 % |
| Axle height | 17.32" | 17.09" | -5.8 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 315/55R21. Fit 335/50R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.6 mph | -0.4 |
| 50 mph | 49.3 mph | -0.7 |
| 70 mph | 69.1 mph | -0.9 |
| 90 mph | 88.8 mph | -1.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,869 on the road, so it over-counts by 131. At a true 70 mph the first turns 679 times a minute, the second 688.