Tire Size Box

315/25R19 vs 305/30R19

305/30R19 compared with 315/25R19

+4.0% diameter, −0.4" width

305/30R19 is 26.20" tall vs 25.20". More than the 3% rule of thumb, so check carefully before switching.

25.2"19" rim3.1"12.4" wide
315/25R19 (solid) compared with 305/30R19 (dashed outline), drawn to scale

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

62.4 mph

305/30R19 is +1.00 inches (+4.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/25R19305/30R19Difference%
Overall diameter25.20"26.20"+1.00"+4.0%
Section width12.40"12.01"−0.39"−3.2%
Sidewall height3.10"3.60"+0.50"+16.2%
Circumference79.17"82.32"+3.15"+4.0%
Revolutions per mile800.3769.6−30.7−3.8%

Speedometer difference

If your vehicle came with 315/25R19 and you fit 305/30R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.8 mph+0.8 mph
30 mph31.2 mph+1.2 mph
40 mph41.6 mph+1.6 mph
50 mph52.0 mph+2.0 mph
60 mph62.4 mph+2.4 mph
65 mph67.6 mph+2.6 mph
70 mph72.8 mph+2.8 mph
75 mph78.0 mph+3.0 mph
80 mph83.2 mph+3.2 mph

Each size on its own

Questions

Which is bigger, 315/25R19 or 305/30R19?
305/30R19 is taller by 1.00 inches (26.20" vs 25.20"). 315/25R19 is wider by 0.39 inches.
Can I replace 315/25R19 with 305/30R19?
It is not recommended without checking carefully. The diameter difference is +4.0%, 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 315/25R19), your real speed is 62.4 mph. Your odometer will under-count miles by about 4.0%.
Will 305/30R19 lift my vehicle?
Ride height changes by half the diameter difference: +0.50 inches of ground clearance at the axle.

Other comparisons