335/35R21 vs 355/30R21
Going from one to the other changes the overall height by -2.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/35R21 | 355/30R21 | Change |
|---|---|---|---|
| Overall height | 30.2" | 29.4" | -2.8 % |
| Sidewall | 4.62" | 4.19" | -9.2 % |
| Section width | 335 mm | 355 mm | +6.0 % |
| Circumference | 95.0" | 92.3" | -2.8 % |
| Revs per mile | 667 | 686 | +2.8 % |
| Axle height | 15.12" | 14.69" | -10.8 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 335/35R21. Fit 355/30R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.2 mph | -0.8 |
| 50 mph | 48.6 mph | -1.4 |
| 70 mph | 68.0 mph | -2.0 |
| 90 mph | 87.5 mph | -2.5 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,720 on the road, so it over-counts by 280. At a true 70 mph the first turns 778 times a minute, the second 801.