355/60R21 vs 335/60R21
Going from one to the other changes the overall height by -2.5 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 355/60R21 | 335/60R21 | Change |
|---|---|---|---|
| Overall height | 37.8" | 36.8" | -2.5 % |
| Sidewall | 8.39" | 7.91" | -5.6 % |
| Section width | 355 mm | 335 mm | -5.6 % |
| Circumference | 118.7" | 115.7" | -2.5 % |
| Revs per mile | 534 | 548 | +2.5 % |
| Axle height | 18.89" | 18.41" | -12.0 mm |
| Approved rim width | 10–13" | 9.5–12.5" | overlap 10–12.5" |
Both are approved on a rim 10" to 12.5" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 355/60R21. Fit 335/60R21 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 9,750 on the road, so it over-counts by 250. At a true 70 mph the first turns 623 times a minute, the second 639.