335/55R21 vs 355/55R21
Going from one to the other changes the overall height by +2.4 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/55R21 | 355/55R21 | Change |
|---|---|---|---|
| Overall height | 35.5" | 36.4" | +2.4 % |
| Sidewall | 7.25" | 7.69" | +6.0 % |
| Section width | 335 mm | 355 mm | +6.0 % |
| Circumference | 111.6" | 114.3" | +2.4 % |
| Revs per mile | 568 | 554 | -2.4 % |
| Axle height | 17.75" | 18.19" | +11.0 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 335/55R21. Fit 355/55R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.7 mph | +0.7 |
| 50 mph | 51.2 mph | +1.2 |
| 70 mph | 71.7 mph | +1.7 |
| 90 mph | 92.2 mph | +2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,244 on the road, so it under-counts by 244. At a true 70 mph the first turns 663 times a minute, the second 647.