Tire Size Box

295/25R21 vs 285/30R21

285/30R21 compared with 295/25R21

+3.5% diameter, −0.4" width

285/30R21 is 27.73" tall vs 26.81". More than the 3% rule of thumb, so check carefully before switching.

26.8"21" rim2.9"11.6" wide
295/25R21 (solid) compared with 285/30R21 (dashed outline), drawn to scale

With 285/30R21 tires, when your speedometer says 60 mph you are really going

62.1 mph

285/30R21 is +0.93 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/25R21285/30R21Difference%
Overall diameter26.81"27.73"+0.93"+3.5%
Section width11.61"11.22"−0.39"−3.4%
Sidewall height2.90"3.37"+0.46"+15.9%
Circumference84.22"87.12"+2.91"+3.5%
Revolutions per mile752.3727.2−25.1−3.3%

Speedometer difference

If your vehicle came with 295/25R21 and you fit 285/30R21, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.2 mph+2.2 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 295/25R21 or 285/30R21?
285/30R21 is taller by 0.93 inches (27.73" vs 26.81"). 295/25R21 is wider by 0.39 inches.
Can I replace 295/25R21 with 285/30R21?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 285/30R21 change my speedometer?
When your speedometer reads 60 mph with 285/30R21 fitted (calibrated for 295/25R21), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 285/30R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.46 inches of ground clearance at the axle.

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