Tire Size Box

225/25R21 vs 225/30R21

225/30R21 compared with 225/25R21

+3.5% diameter, 0.0" width

225/30R21 is 26.31" tall vs 25.43". More than the 3% rule of thumb, so check carefully before switching.

25.4"21" rim2.2"8.9" wide
225/25R21 (solid) compared with 225/30R21 (dashed outline), drawn to scale

With 225/30R21 tires, when your speedometer says 60 mph you are really going

62.1 mph

225/30R21 is +0.89 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

225/25R21225/30R21Difference%
Overall diameter25.43"26.31"+0.89"+3.5%
Section width8.86"8.86"0.00"0.0%
Sidewall height2.21"2.66"+0.44"+20.0%
Circumference79.89"82.67"+2.78"+3.5%
Revolutions per mile793.1766.4−26.7−3.4%

Speedometer difference

If your vehicle came with 225/25R21 and you fit 225/30R21, 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 mph67.3 mph+2.3 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, 225/25R21 or 225/30R21?
225/30R21 is taller by 0.89 inches (26.31" vs 25.43"). 225/25R21 is the same width.
Can I replace 225/25R21 with 225/30R21?
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 225/30R21 change my speedometer?
When your speedometer reads 60 mph with 225/30R21 fitted (calibrated for 225/25R21), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 225/30R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.44 inches of ground clearance at the axle.

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