345/50R21 vs 335/55R21
Going from one to the other changes the overall height by +2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/50R21 | 335/55R21 | Change |
|---|---|---|---|
| Overall height | 34.6" | 35.5" | +2.7 % |
| Sidewall | 6.79" | 7.25" | +6.8 % |
| Section width | 345 mm | 335 mm | -2.9 % |
| Circumference | 108.6" | 111.6" | +2.7 % |
| Revs per mile | 583 | 568 | -2.7 % |
| Axle height | 17.29" | 17.75" | +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 345/50R21. Fit 335/55R21 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 | 71.9 mph | +1.9 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,268 on the road, so it under-counts by 268. At a true 70 mph the first turns 680 times a minute, the second 663.