335/65R21 vs 345/60R21
Going from one to the other changes the overall height by -2.2 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/65R21 | 345/60R21 | Change |
|---|---|---|---|
| Overall height | 38.1" | 37.3" | -2.2 % |
| Sidewall | 8.57" | 8.15" | -4.9 % |
| Section width | 335 mm | 345 mm | +3.0 % |
| Circumference | 119.8" | 117.2" | -2.2 % |
| Revs per mile | 529 | 541 | +2.2 % |
| Axle height | 19.07" | 18.65" | -10.8 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 335/65R21. Fit 345/60R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.9 mph | -1.1 |
| 70 mph | 68.4 mph | -1.6 |
| 90 mph | 88.0 mph | -2.0 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,778 on the road, so it over-counts by 222. At a true 70 mph the first turns 617 times a minute, the second 631.