Tire Size Box

255/30R19 vs 255/40R19

255/40R19 compared with 255/30R19

+8.0% diameter, 0.0" width

255/40R19 is 27.03" tall vs 25.02". More than the 3% rule of thumb, so check carefully before switching.

25.0"19" rim3.0"10.0" wide
255/30R19 (solid) compared with 255/40R19 (dashed outline), drawn to scale

With 255/40R19 tires, when your speedometer says 60 mph you are really going

64.8 mph

255/40R19 is +2.01 inches (+8.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

255/30R19255/40R19Difference%
Overall diameter25.02"27.03"+2.01"+8.0%
Section width10.04"10.04"0.00"0.0%
Sidewall height3.01"4.02"+1.00"+33.3%
Circumference78.61"84.92"+6.31"+8.0%
Revolutions per mile806.0746.1−59.9−7.4%

Speedometer difference

If your vehicle came with 255/30R19 and you fit 255/40R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.2 mph+3.2 mph
50 mph54.0 mph+4.0 mph
60 mph64.8 mph+4.8 mph
65 mph70.2 mph+5.2 mph
70 mph75.6 mph+5.6 mph
75 mph81.0 mph+6.0 mph
80 mph86.4 mph+6.4 mph

Each size on its own

Questions

Which is bigger, 255/30R19 or 255/40R19?
255/40R19 is taller by 2.01 inches (27.03" vs 25.02"). 255/30R19 is the same width.
Can I replace 255/30R19 with 255/40R19?
It is not recommended without checking carefully. The diameter difference is +8.0%, 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 255/40R19 change my speedometer?
When your speedometer reads 60 mph with 255/40R19 fitted (calibrated for 255/30R19), your real speed is 64.8 mph. Your odometer will under-count miles by about 8.0%.
Will 255/40R19 lift my vehicle?
Ride height changes by half the diameter difference: +1.00 inches of ground clearance at the axle.

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