Tire Size Box

285/30R21 vs 275/35R21

275/35R21 compared with 285/30R21

+3.1% diameter, −0.4" width

275/35R21 is 28.58" tall vs 27.73". More than the 3% rule of thumb, so check carefully before switching.

27.7"21" rim3.4"11.2" wide
285/30R21 (solid) compared with 275/35R21 (dashed outline), drawn to scale

With 275/35R21 tires, when your speedometer says 60 mph you are really going

61.8 mph

275/35R21 is +0.85 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/30R21275/35R21Difference%
Overall diameter27.73"28.58"+0.85"+3.1%
Section width11.22"10.83"−0.39"−3.5%
Sidewall height3.37"3.79"+0.42"+12.6%
Circumference87.12"89.78"+2.66"+3.1%
Revolutions per mile727.2705.7−21.5−3.0%

Speedometer difference

If your vehicle came with 285/30R21 and you fit 275/35R21, 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 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.1 mph+2.1 mph
75 mph77.3 mph+2.3 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 285/30R21 or 275/35R21?
275/35R21 is taller by 0.85 inches (28.58" vs 27.73"). 285/30R21 is wider by 0.39 inches.
Can I replace 285/30R21 with 275/35R21?
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 275/35R21 change my speedometer?
When your speedometer reads 60 mph with 275/35R21 fitted (calibrated for 285/30R21), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.1%.
Will 275/35R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.42 inches of ground clearance at the axle.

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