QuickCheckToolsTire size calculator › 325/65R18 vs 35x12.50R18
325/65R18 vs 35x12.50R18
35x12.50R18 is 0.4 inches (1.1%) taller than 325/65R18 and 0.3 inches narrower. Ground clearance changes by about 0.2 inches, and at an indicated 60 mph you would actually be doing 60.6 mph.
35x12.50R18 is 1.1% taller
That's within the usual 3% guideline for replacing a tire size.
| 325/65R18 | 35x12.50R18 | Difference | |
|---|---|---|---|
| Overall diameter | 34.6 in | 35.0 in | +0.4 in |
| Width | 12.8 in | 12.5 in | -0.3 in |
| Sidewall height | 8.3 in | 8.5 in | +0.2 in |
| Circumference | 108.8 in | 110.0 in | +1.2 in |
| Revolutions per mile | 582 | 576 | -6 |
Speedometer with 35x12.50R18 fitted (calibrated for 325/65R18)
| Speedometer shows | Actual speed |
|---|---|
| 20 mph | 20.2 mph |
| 30 mph | 30.3 mph |
| 40 mph | 40.4 mph |
| 50 mph | 50.5 mph |
| 60 mph | 60.6 mph |
| 70 mph | 70.7 mph |
| 80 mph | 80.8 mph |
Open this comparison in the calculator
What the difference means
Diameter is what matters most. A taller tire raises the vehicle by half the difference, here about 0.2 inches, and covers more ground per turn, so the speedometer reads lower than your real speed. Width changes how much tread meets the road and whether the tire clears suspension parts and wheel arches.
These are design dimensions calculated from the sizes. Actual tires vary slightly by brand and model, so check fitment for your vehicle before buying.