335/60R21 vs 355/60R21
Going from one to the other changes the overall height by +2.6 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/60R21 | 355/60R21 | Change |
|---|---|---|---|
| Overall height | 36.8" | 37.8" | +2.6 % |
| Sidewall | 7.91" | 8.39" | +6.0 % |
| Section width | 335 mm | 355 mm | +6.0 % |
| Circumference | 115.7" | 118.7" | +2.6 % |
| Revs per mile | 548 | 534 | -2.6 % |
| Axle height | 18.41" | 18.89" | +12.0 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 335/60R21. Fit 355/60R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.8 mph | +0.8 |
| 50 mph | 51.3 mph | +1.3 |
| 70 mph | 71.8 mph | +1.8 |
| 90 mph | 92.3 mph | +2.3 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,257 on the road, so it under-counts by 257. At a true 70 mph the first turns 639 times a minute, the second 623.