Tire Size Box

285/35R21 vs 285/45R21

285/45R21 compared with 285/35R21

+7.8% diameter, 0.0" width

285/45R21 is 31.10" tall vs 28.85". More than the 3% rule of thumb, so check carefully before switching.

28.9"21" rim3.9"11.2" wide
285/35R21 (solid) compared with 285/45R21 (dashed outline), drawn to scale

With 285/45R21 tires, when your speedometer says 60 mph you are really going

64.7 mph

285/45R21 is +2.24 inches (+7.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/35R21285/45R21Difference%
Overall diameter28.85"31.10"+2.24"+7.8%
Section width11.22"11.22"0.00"0.0%
Sidewall height3.93"5.05"+1.12"+28.6%
Circumference90.65"97.70"+7.05"+7.8%
Revolutions per mile699.0648.5−50.4−7.2%

Speedometer difference

If your vehicle came with 285/35R21 and you fit 285/45R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.3 mph+2.3 mph
40 mph43.1 mph+3.1 mph
50 mph53.9 mph+3.9 mph
60 mph64.7 mph+4.7 mph
65 mph70.1 mph+5.1 mph
70 mph75.4 mph+5.4 mph
75 mph80.8 mph+5.8 mph
80 mph86.2 mph+6.2 mph

Each size on its own

Questions

Which is bigger, 285/35R21 or 285/45R21?
285/45R21 is taller by 2.24 inches (31.10" vs 28.85"). 285/35R21 is the same width.
Can I replace 285/35R21 with 285/45R21?
It is not recommended without checking carefully. The diameter difference is +7.8%, 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 285/45R21 change my speedometer?
When your speedometer reads 60 mph with 285/45R21 fitted (calibrated for 285/35R21), your real speed is 64.7 mph. Your odometer will under-count miles by about 7.8%.
Will 285/45R21 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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