335/25R18 vs 345/25R18
Going from one to the other changes the overall height by +0.8 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 335/25R18 | 345/25R18 | Change |
|---|---|---|---|
| Overall height | 24.6" | 24.8" | +0.8 % |
| Sidewall | 3.30" | 3.40" | +3.0 % |
| Section width | 335 mm | 345 mm | +3.0 % |
| Circumference | 77.3" | 77.9" | +0.8 % |
| Revs per mile | 820 | 814 | -0.8 % |
| Axle height | 12.30" | 12.40" | +2.5 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 335/25R18. Fit 345/25R18 and the needle stops telling the truth.
| Needle says | You are doing | Out by |
|---|---|---|
| 30 mph | 30.2 mph | +0.2 |
| 50 mph | 50.4 mph | +0.4 |
| 70 mph | 70.6 mph | +0.6 |
| 90 mph | 90.7 mph | +0.7 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,080 on the road, so it under-counts by 80. At a true 70 mph the first turns 957 times a minute, the second 949.