345/45R21 vs 335/45R21
Going from one to the other changes the overall height by -1.1 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/45R21 | 335/45R21 | Change |
|---|---|---|---|
| Overall height | 33.2" | 32.9" | -1.1 % |
| Sidewall | 6.11" | 5.94" | -2.9 % |
| Section width | 345 mm | 335 mm | -2.9 % |
| Circumference | 104.4" | 103.3" | -1.1 % |
| Revs per mile | 607 | 614 | +1.1 % |
| Axle height | 16.61" | 16.44" | -4.5 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 335/45R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.7 mph | -0.3 |
| 50 mph | 49.5 mph | -0.5 |
| 70 mph | 69.3 mph | -0.7 |
| 90 mph | 89.0 mph | -1.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,893 on the road, so it over-counts by 107. At a true 70 mph the first turns 708 times a minute, the second 716.