345/45R21 vs 335/50R21
Going from one to the other changes the overall height by +2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/45R21 | 335/50R21 | Change |
|---|---|---|---|
| Overall height | 33.2" | 34.2" | +2.9 % |
| Sidewall | 6.11" | 6.59" | +7.9 % |
| Section width | 345 mm | 335 mm | -2.9 % |
| Circumference | 104.4" | 107.4" | +2.9 % |
| Revs per mile | 607 | 590 | -2.9 % |
| Axle height | 16.61" | 17.09" | +12.3 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 345/45R21. Fit 335/50R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.5 mph | +1.5 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,290 on the road, so it under-counts by 290. At a true 70 mph the first turns 708 times a minute, the second 688.