Tire Size Box

295/25R21 vs 295/30R21

295/30R21 compared with 295/25R21

+4.3% diameter, 0.0" width

295/30R21 is 27.97" 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 295/30R21 (dashed outline), drawn to scale

With 295/30R21 tires, when your speedometer says 60 mph you are really going

62.6 mph

295/30R21 is +1.16 inches (+4.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

295/25R21295/30R21Difference%
Overall diameter26.81"27.97"+1.16"+4.3%
Section width11.61"11.61"0.00"0.0%
Sidewall height2.90"3.48"+0.58"+20.0%
Circumference84.22"87.87"+3.65"+4.3%
Revolutions per mile752.3721.1−31.2−4.2%

Speedometer difference

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

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.0 mph+3.0 mph
75 mph78.2 mph+3.2 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 295/25R21 or 295/30R21?
295/30R21 is taller by 1.16 inches (27.97" vs 26.81"). 295/25R21 is the same width.
Can I replace 295/25R21 with 295/30R21?
It is not recommended without checking carefully. The diameter difference is +4.3%, 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 295/30R21 change my speedometer?
When your speedometer reads 60 mph with 295/30R21 fitted (calibrated for 295/25R21), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.3%.
Will 295/30R21 lift my vehicle?
Ride height changes by half the diameter difference: +0.58 inches of ground clearance at the axle.

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