315/60R21 vs 335/55R21
Going from one to the other changes the overall height by -1.0 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 315/60R21 | 335/55R21 | Change |
|---|---|---|---|
| Overall height | 35.9" | 35.5" | -1.0 % |
| Sidewall | 7.44" | 7.25" | -2.5 % |
| Section width | 315 mm | 335 mm | +6.3 % |
| Circumference | 112.7" | 111.6" | -1.0 % |
| Revs per mile | 562 | 568 | +1.0 % |
| Axle height | 17.94" | 17.75" | -4.8 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 315/60R21. Fit 335/55R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.3 mph | -0.7 |
| 90 mph | 89.1 mph | -0.9 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,896 on the road, so it over-counts by 104. At a true 70 mph the first turns 656 times a minute, the second 663.