335/35R21 vs 345/35R21
Going from one to the other changes the overall height by +0.9 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/35R21 | 345/35R21 | Change |
|---|---|---|---|
| Overall height | 30.2" | 30.5" | +0.9 % |
| Sidewall | 4.62" | 4.75" | +3.0 % |
| Section width | 335 mm | 345 mm | +3.0 % |
| Circumference | 95.0" | 95.8" | +0.9 % |
| Revs per mile | 667 | 661 | -0.9 % |
| Axle height | 15.12" | 15.25" | +3.5 mm |
| Approved rim width | 9.5–12.5" | 9.5–12.5" | overlap 9.5–12.5" |
Both are approved on a rim 9.5" 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 345/35R21 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.3 mph | +0.3 |
| 50 mph | 50.5 mph | +0.5 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.8 mph | +0.8 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,091 on the road, so it under-counts by 91. At a true 70 mph the first turns 778 times a minute, the second 771.