335/30R21 vs 345/30R21
Going from one to the other changes the overall height by +0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/30R21 | 345/30R21 | Change |
|---|---|---|---|
| Overall height | 28.9" | 29.1" | +0.8 % |
| Sidewall | 3.96" | 4.07" | +3.0 % |
| Section width | 335 mm | 345 mm | +3.0 % |
| Circumference | 90.8" | 91.6" | +0.8 % |
| Revs per mile | 698 | 692 | -0.8 % |
| Axle height | 14.46" | 14.57" | +3.0 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 335/30R21. Fit 345/30R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.7 mph | +0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,082 on the road, so it under-counts by 82. At a true 70 mph the first turns 814 times a minute, the second 807.