Tire Size Box

305/25R20 vs 295/30R20

295/30R20 compared with 305/25R20

+3.7% diameter, −0.4" width

295/30R20 is 26.97" tall vs 26.00". More than the 3% rule of thumb, so check carefully before switching.

26.0"20" rim3.0"12.0" wide
305/25R20 (solid) compared with 295/30R20 (dashed outline), drawn to scale

With 295/30R20 tires, when your speedometer says 60 mph you are really going

62.2 mph

295/30R20 is +0.96 inches (+3.7%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/25R20295/30R20Difference%
Overall diameter26.00"26.97"+0.96"+3.7%
Section width12.01"11.61"−0.39"−3.3%
Sidewall height3.00"3.48"+0.48"+16.1%
Circumference81.69"84.72"+3.03"+3.7%
Revolutions per mile775.6747.8−27.7−3.6%

Speedometer difference

If your vehicle came with 305/25R20 and you fit 295/30R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.1 mph+1.1 mph
40 mph41.5 mph+1.5 mph
50 mph51.9 mph+1.9 mph
60 mph62.2 mph+2.2 mph
65 mph67.4 mph+2.4 mph
70 mph72.6 mph+2.6 mph
75 mph77.8 mph+2.8 mph
80 mph83.0 mph+3.0 mph

Each size on its own

Questions

Which is bigger, 305/25R20 or 295/30R20?
295/30R20 is taller by 0.96 inches (26.97" vs 26.00"). 305/25R20 is wider by 0.39 inches.
Can I replace 305/25R20 with 295/30R20?
It is not recommended without checking carefully. The diameter difference is +3.7%, 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 295/30R20 change my speedometer?
When your speedometer reads 60 mph with 295/30R20 fitted (calibrated for 305/25R20), your real speed is 62.2 mph. Your odometer will under-count miles by about 3.7%.
Will 295/30R20 lift my vehicle?
Ride height changes by half the diameter difference: +0.48 inches of ground clearance at the axle.

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