Tire Size Box

285/35R20 vs 285/45R20

285/45R20 compared with 285/35R20

+8.1% diameter, 0.0" width

285/45R20 is 30.10" tall vs 27.85". More than the 3% rule of thumb, so check carefully before switching.

27.9"20" rim3.9"11.2" wide
285/35R20 (solid) compared with 285/45R20 (dashed outline), drawn to scale

With 285/45R20 tires, when your speedometer says 60 mph you are really going

64.8 mph

285/45R20 is +2.24 inches (+8.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/35R20285/45R20Difference%
Overall diameter27.85"30.10"+2.24"+8.1%
Section width11.22"11.22"0.00"0.0%
Sidewall height3.93"5.05"+1.12"+28.6%
Circumference87.51"94.56"+7.05"+8.1%
Revolutions per mile724.1670.1−54.0−7.5%

Speedometer difference

If your vehicle came with 285/35R20 and you fit 285/45R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.2 mph+3.2 mph
50 mph54.0 mph+4.0 mph
60 mph64.8 mph+4.8 mph
65 mph70.2 mph+5.2 mph
70 mph75.6 mph+5.6 mph
75 mph81.0 mph+6.0 mph
80 mph86.4 mph+6.4 mph

Each size on its own

Questions

Which is bigger, 285/35R20 or 285/45R20?
285/45R20 is taller by 2.24 inches (30.10" vs 27.85"). 285/35R20 is the same width.
Can I replace 285/35R20 with 285/45R20?
It is not recommended without checking carefully. The diameter difference is +8.1%, 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 285/45R20 change my speedometer?
When your speedometer reads 60 mph with 285/45R20 fitted (calibrated for 285/35R20), your real speed is 64.8 mph. Your odometer will under-count miles by about 8.1%.
Will 285/45R20 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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