325/30R18 vs 335/30R18
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 | 325/30R18 | 335/30R18 | Change |
|---|---|---|---|
| Overall height | 25.7" | 25.9" | +0.9 % |
| Sidewall | 3.84" | 3.96" | +3.1 % |
| Section width | 325 mm | 335 mm | +3.1 % |
| Circumference | 80.7" | 81.4" | +0.9 % |
| Revs per mile | 785 | 778 | -0.9 % |
| Axle height | 12.84" | 12.96" | +3.0 mm |
| Approved rim width | 9–12" | 9.5–12.5" | overlap 9.5–12" |
Both are approved on a rim 9.5" to 12" wide. If yours is in that band, this is a tire change and nothing else.
What the speedometer will say
Calibrated for 325/30R18. Fit 335/30R18 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 10,092 on the road, so it under-counts by 92. At a true 70 mph the first turns 916 times a minute, the second 908.