325/55R21 vs 335/50R21
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 | 325/55R21 | 335/50R21 | Change |
|---|---|---|---|
| Overall height | 35.1" | 34.2" | -2.5 % |
| Sidewall | 7.04" | 6.59" | -6.3 % |
| Section width | 325 mm | 335 mm | +3.1 % |
| Circumference | 110.2" | 107.4" | -2.5 % |
| Revs per mile | 575 | 590 | +2.5 % |
| Axle height | 17.54" | 17.09" | -11.3 mm |
| Approved rim width | 9–12" | 9.5–12.5" | overlap 9.5–12" |
Both are approved on a rim 9.5" to 12" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 325/55R21. Fit 335/50R21 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 9,747 on the road, so it over-counts by 253. At a true 70 mph the first turns 671 times a minute, the second 688.