335/50R21 vs 325/55R21
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/50R21 | 325/55R21 | Change |
|---|---|---|---|
| Overall height | 34.2" | 35.1" | +2.6 % |
| Sidewall | 6.59" | 7.04" | +6.7 % |
| Section width | 335 mm | 325 mm | -3.0 % |
| Circumference | 107.4" | 110.2" | +2.6 % |
| Revs per mile | 590 | 575 | -2.6 % |
| Axle height | 17.09" | 17.54" | +11.3 mm |
| Approved rim width | 9.5–12.5" | 9–12" | 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 335/50R21. Fit 325/55R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,259 on the road, so it under-counts by 259. At a true 70 mph the first turns 688 times a minute, the second 671.