Tire Size Box

305/25R19 vs 305/30R19

305/30R19 compared with 305/25R19

+4.8% diameter, 0.0" width

305/30R19 is 26.20" tall vs 25.00". More than the 3% rule of thumb, so check carefully before switching.

25.0"19" rim3.0"12.0" wide
305/25R19 (solid) compared with 305/30R19 (dashed outline), drawn to scale

With 305/30R19 tires, when your speedometer says 60 mph you are really going

62.9 mph

305/30R19 is +1.20 inches (+4.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/25R19305/30R19Difference%
Overall diameter25.00"26.20"+1.20"+4.8%
Section width12.01"12.01"0.00"0.0%
Sidewall height3.00"3.60"+0.60"+20.0%
Circumference78.55"82.32"+3.77"+4.8%
Revolutions per mile806.6769.6−37.0−4.6%

Speedometer difference

If your vehicle came with 305/25R19 and you fit 305/30R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.0 mph+1.0 mph
30 mph31.4 mph+1.4 mph
40 mph41.9 mph+1.9 mph
50 mph52.4 mph+2.4 mph
60 mph62.9 mph+2.9 mph
65 mph68.1 mph+3.1 mph
70 mph73.4 mph+3.4 mph
75 mph78.6 mph+3.6 mph
80 mph83.8 mph+3.8 mph

Each size on its own

Questions

Which is bigger, 305/25R19 or 305/30R19?
305/30R19 is taller by 1.20 inches (26.20" vs 25.00"). 305/25R19 is the same width.
Can I replace 305/25R19 with 305/30R19?
It is not recommended without checking carefully. The diameter difference is +4.8%, 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 305/30R19 change my speedometer?
When your speedometer reads 60 mph with 305/30R19 fitted (calibrated for 305/25R19), your real speed is 62.9 mph. Your odometer will under-count miles by about 4.8%.
Will 305/30R19 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

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