345/55R18 vs 335/60R18
Going from one to the other changes the overall height by +2.7 %. That is inside the 3% band, so it fits and the speedometer stays close.
Side by side
| Measure | 345/55R18 | 335/60R18 | Change |
|---|---|---|---|
| Overall height | 32.9" | 33.8" | +2.7 % |
| Sidewall | 7.47" | 7.91" | +5.9 % |
| Section width | 345 mm | 335 mm | -2.9 % |
| Circumference | 103.5" | 106.3" | +2.7 % |
| Revs per mile | 612 | 596 | -2.7 % |
| Axle height | 16.47" | 16.91" | +11.3 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 345/55R18. Fit 335/60R18 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 | 71.9 mph | +1.9 |
| 90 mph | 92.4 mph | +2.4 |
The odometer drifts with it. Ten thousand miles on the dial are really 10,269 on the road, so it under-counts by 269. At a true 70 mph the first turns 714 times a minute, the second 696.