Tire Size Box

315/25R22 vs 305/30R22

305/30R22 compared with 315/25R22

+3.6% diameter, −0.4" width

305/30R22 is 29.20" tall vs 28.20". More than the 3% rule of thumb, so check carefully before switching.

28.2"22" rim3.1"12.4" wide
315/25R22 (solid) compared with 305/30R22 (dashed outline), drawn to scale

With 305/30R22 tires, when your speedometer says 60 mph you are really going

62.1 mph

305/30R22 is +1.00 inches (+3.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/25R22305/30R22Difference%
Overall diameter28.20"29.20"+1.00"+3.6%
Section width12.40"12.01"−0.39"−3.2%
Sidewall height3.10"3.60"+0.50"+16.2%
Circumference88.60"91.75"+3.15"+3.6%
Revolutions per mile715.2690.6−24.6−3.4%

Speedometer difference

If your vehicle came with 315/25R22 and you fit 305/30R22, 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 mph41.4 mph+1.4 mph
50 mph51.8 mph+1.8 mph
60 mph62.1 mph+2.1 mph
65 mph67.3 mph+2.3 mph
70 mph72.5 mph+2.5 mph
75 mph77.7 mph+2.7 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 315/25R22 or 305/30R22?
305/30R22 is taller by 1.00 inches (29.20" vs 28.20"). 315/25R22 is wider by 0.39 inches.
Can I replace 315/25R22 with 305/30R22?
It is not recommended without checking carefully. The diameter difference is +3.6%, 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 305/30R22 change my speedometer?
When your speedometer reads 60 mph with 305/30R22 fitted (calibrated for 315/25R22), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.6%.
Will 305/30R22 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

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