Tire Size Box

305/40R19 vs 305/50R19

305/50R19 compared with 305/40R19

+8.4% diameter, 0.0" width

305/50R19 is 31.01" tall vs 28.61". More than the 3% rule of thumb, so check carefully before switching.

28.6"19" rim4.8"12.0" wide
305/40R19 (solid) compared with 305/50R19 (dashed outline), drawn to scale

With 305/50R19 tires, when your speedometer says 60 mph you are really going

65.0 mph

305/50R19 is +2.40 inches (+8.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/40R19305/50R19Difference%
Overall diameter28.61"31.01"+2.40"+8.4%
Section width12.01"12.01"0.00"0.0%
Sidewall height4.80"6.00"+1.20"+25.0%
Circumference89.87"97.41"+7.54"+8.4%
Revolutions per mile705.0650.4−54.6−7.7%

Speedometer difference

If your vehicle came with 305/40R19 and you fit 305/50R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.7 mph+1.7 mph
30 mph32.5 mph+2.5 mph
40 mph43.4 mph+3.4 mph
50 mph54.2 mph+4.2 mph
60 mph65.0 mph+5.0 mph
65 mph70.5 mph+5.5 mph
70 mph75.9 mph+5.9 mph
75 mph81.3 mph+6.3 mph
80 mph86.7 mph+6.7 mph

Each size on its own

Questions

Which is bigger, 305/40R19 or 305/50R19?
305/50R19 is taller by 2.40 inches (31.01" vs 28.61"). 305/40R19 is the same width.
Can I replace 305/40R19 with 305/50R19?
It is not recommended without checking carefully. The diameter difference is +8.4%, 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 305/50R19 change my speedometer?
When your speedometer reads 60 mph with 305/50R19 fitted (calibrated for 305/40R19), your real speed is 65.0 mph. Your odometer will under-count miles by about 8.4%.
Will 305/50R19 lift my vehicle?
Ride height changes by half the diameter difference: +1.20 inches of ground clearance at the axle.

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