335/55R21 vs 345/50R21
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 | 335/55R21 | 345/50R21 | Change |
|---|---|---|---|
| Overall height | 35.5" | 34.6" | -2.6 % |
| Sidewall | 7.25" | 6.79" | -6.4 % |
| Section width | 335 mm | 345 mm | +3.0 % |
| Circumference | 111.6" | 108.6" | -2.6 % |
| Revs per mile | 568 | 583 | +2.6 % |
| Axle height | 17.75" | 17.29" | -11.8 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 335/55R21. Fit 345/50R21 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 9,739 on the road, so it over-counts by 261. At a true 70 mph the first turns 663 times a minute, the second 680.