Tire Size Box

335/45R18 vs 325/50R18

325/50R18 compared with 335/45R18

+3.1% diameter, −0.4" width

325/50R18 is 30.80" tall vs 29.87". More than the 3% rule of thumb, so check carefully before switching.

29.9"18" rim5.9"13.2" wide
335/45R18 (solid) compared with 325/50R18 (dashed outline), drawn to scale

With 325/50R18 tires, when your speedometer says 60 mph you are really going

61.9 mph

325/50R18 is +0.93 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

335/45R18325/50R18Difference%
Overall diameter29.87"30.80"+0.93"+3.1%
Section width13.19"12.80"−0.39"−3.0%
Sidewall height5.94"6.40"+0.46"+7.8%
Circumference93.84"96.75"+2.91"+3.1%
Revolutions per mile675.2654.9−20.3−3.0%

Speedometer difference

If your vehicle came with 335/45R18 and you fit 325/50R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 335/45R18 or 325/50R18?
325/50R18 is taller by 0.93 inches (30.80" vs 29.87"). 335/45R18 is wider by 0.39 inches.
Can I replace 335/45R18 with 325/50R18?
It is not recommended without checking carefully. The diameter difference is +3.1%, more than the 3% most shops and makers allow. It will throw off the speedometer and may affect ABS, stability control and clearance.
How much will 325/50R18 change my speedometer?
When your speedometer reads 60 mph with 325/50R18 fitted (calibrated for 335/45R18), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 325/50R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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