335/30R21 vs 355/30R21
Going from one to the other changes the overall height by +1.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/30R21 | 355/30R21 | Change |
|---|---|---|---|
| Overall height | 28.9" | 29.4" | +1.6 % |
| Sidewall | 3.96" | 4.19" | +6.0 % |
| Section width | 335 mm | 355 mm | +6.0 % |
| Circumference | 90.8" | 92.3" | +1.6 % |
| Revs per mile | 698 | 686 | -1.6 % |
| Axle height | 14.46" | 14.69" | +6.0 mm |
| Approved rim width | 9.5–12.5" | 10–13" | overlap 10–12.5" |
Both are approved on a rim 10" 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 355/30R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.5 mph | +0.5 |
| 50 mph | 50.8 mph | +0.8 |
| 70 mph | 71.1 mph | +1.1 |
| 90 mph | 91.5 mph | +1.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,163 on the road, so it under-counts by 163. At a true 70 mph the first turns 814 times a minute, the second 801.