335/60R21 vs 325/65R21
Going from one to the other changes the overall height by +2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/60R21 | 325/65R21 | Change |
|---|---|---|---|
| Overall height | 36.8" | 37.6" | +2.2 % |
| Sidewall | 7.91" | 8.32" | +5.1 % |
| Section width | 335 mm | 325 mm | -3.0 % |
| Circumference | 115.7" | 118.2" | +2.2 % |
| Revs per mile | 548 | 536 | -2.2 % |
| Axle height | 18.41" | 18.82" | +10.3 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 335/60R21. Fit 325/65R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.1 mph | +1.1 |
| 70 mph | 71.5 mph | +1.5 |
| 90 mph | 92.0 mph | +2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,219 on the road, so it under-counts by 219. At a true 70 mph the first turns 639 times a minute, the second 625.