355/45R21 vs 335/50R21
Going from one to the other changes the overall height by +1.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 355/45R21 | 335/50R21 | Change |
|---|---|---|---|
| Overall height | 33.6" | 34.2" | +1.8 % |
| Sidewall | 6.29" | 6.59" | +4.9 % |
| Section width | 355 mm | 335 mm | -5.6 % |
| Circumference | 105.5" | 107.4" | +1.8 % |
| Revs per mile | 601 | 590 | -1.8 % |
| Axle height | 16.79" | 17.09" | +7.8 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 355/45R21. Fit 335/50R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.9 mph | +0.9 |
| 70 mph | 71.3 mph | +1.3 |
| 90 mph | 91.6 mph | +1.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,182 on the road, so it under-counts by 182. At a true 70 mph the first turns 701 times a minute, the second 688.