335/40R21 vs 355/35R21
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 | 335/40R21 | 355/35R21 | Change |
|---|---|---|---|
| Overall height | 31.6" | 30.8" | -2.4 % |
| Sidewall | 5.28" | 4.89" | -7.3 % |
| Section width | 335 mm | 355 mm | +6.0 % |
| Circumference | 99.1" | 96.7" | -2.4 % |
| Revs per mile | 639 | 655 | +2.4 % |
| Axle height | 15.78" | 15.39" | -9.8 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 335/40R21. Fit 355/35R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.3 mph | -0.7 |
| 50 mph | 48.8 mph | -1.2 |
| 70 mph | 68.3 mph | -1.7 |
| 90 mph | 87.8 mph | -2.2 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,757 on the road, so it over-counts by 243. At a true 70 mph the first turns 746 times a minute, the second 764.