345/55R21 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 | 345/55R21 | 335/60R21 | Change |
|---|---|---|---|
| Overall height | 35.9" | 36.8" | +2.5 % |
| Sidewall | 7.47" | 7.91" | +5.9 % |
| Section width | 345 mm | 335 mm | -2.9 % |
| Circumference | 112.9" | 115.7" | +2.5 % |
| Revs per mile | 561 | 548 | -2.5 % |
| Axle height | 17.97" | 18.41" | +11.3 mm |
| Approved rim width | 9.5–12.5" | 9.5–12.5" | overlap 9.5–12.5" |
Both are approved on a rim 9.5" 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 345/55R21. Fit 335/60R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.7 mph | +1.7 |
| 90 mph | 92.2 mph | +2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,246 on the road, so it under-counts by 246. At a true 70 mph the first turns 655 times a minute, the second 639.