355/30R21 vs 335/35R21
Going from one to the other changes the overall height by +2.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 355/30R21 | 335/35R21 | Change |
|---|---|---|---|
| Overall height | 29.4" | 30.2" | +2.9 % |
| Sidewall | 4.19" | 4.62" | +10.1 % |
| Section width | 355 mm | 335 mm | -5.6 % |
| Circumference | 92.3" | 95.0" | +2.9 % |
| Revs per mile | 686 | 667 | -2.9 % |
| Axle height | 14.69" | 15.12" | +10.8 mm |
| Approved rim width | 10–13" | 9.5–12.5" | 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 355/30R21. Fit 335/35R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.9 mph | +0.9 |
| 50 mph | 51.4 mph | +1.4 |
| 70 mph | 72.0 mph | +2.0 |
| 90 mph | 92.6 mph | +2.6 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,288 on the road, so it under-counts by 288. At a true 70 mph the first turns 801 times a minute, the second 778.