355/30R24 vs 345/30R24
Going from one to the other changes the overall height by -0.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 355/30R24 | 345/30R24 | Change |
|---|---|---|---|
| Overall height | 32.4" | 32.1" | -0.7 % |
| Sidewall | 4.19" | 4.07" | -2.8 % |
| Section width | 355 mm | 345 mm | -2.8 % |
| Circumference | 101.7" | 101.0" | -0.7 % |
| Revs per mile | 623 | 627 | +0.7 % |
| Axle height | 16.19" | 16.07" | -3.0 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 355/30R24. Fit 345/30R24 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 29.8 mph | -0.2 |
| 50 mph | 49.6 mph | -0.4 |
| 70 mph | 69.5 mph | -0.5 |
| 90 mph | 89.3 mph | -0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 9,927 on the road, so it over-counts by 73. At a true 70 mph the first turns 727 times a minute, the second 732.