Tire Size Box

285/35R18 vs 285/45R18

285/45R18 compared with 285/35R18

+8.7% diameter, 0.0" width

285/45R18 is 28.10" tall vs 25.85". More than the 3% rule of thumb, so check carefully before switching.

25.9"18" rim3.9"11.2" wide
285/35R18 (solid) compared with 285/45R18 (dashed outline), drawn to scale

With 285/45R18 tires, when your speedometer says 60 mph you are really going

65.2 mph

285/45R18 is +2.24 inches (+8.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/35R18285/45R18Difference%
Overall diameter25.85"28.10"+2.24"+8.7%
Section width11.22"11.22"0.00"0.0%
Sidewall height3.93"5.05"+1.12"+28.6%
Circumference81.22"88.27"+7.05"+8.7%
Revolutions per mile780.1717.8−62.3−8.0%

Speedometer difference

If your vehicle came with 285/35R18 and you fit 285/45R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.7 mph+1.7 mph
30 mph32.6 mph+2.6 mph
40 mph43.5 mph+3.5 mph
50 mph54.3 mph+4.3 mph
60 mph65.2 mph+5.2 mph
65 mph70.6 mph+5.6 mph
70 mph76.1 mph+6.1 mph
75 mph81.5 mph+6.5 mph
80 mph86.9 mph+6.9 mph

Each size on its own

Questions

Which is bigger, 285/35R18 or 285/45R18?
285/45R18 is taller by 2.24 inches (28.10" vs 25.85"). 285/35R18 is the same width.
Can I replace 285/35R18 with 285/45R18?
It is not recommended without checking carefully. The diameter difference is +8.7%, 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 285/45R18 change my speedometer?
When your speedometer reads 60 mph with 285/45R18 fitted (calibrated for 285/35R18), your real speed is 65.2 mph. Your odometer will under-count miles by about 8.7%.
Will 285/45R18 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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