Tire Size Box

305/35R19 vs 305/40R19

305/40R19 compared with 305/35R19

+4.4% diameter, 0.0" width

305/40R19 is 28.61" tall vs 27.41". More than the 3% rule of thumb, so check carefully before switching.

27.4"19" rim4.2"12.0" wide
305/35R19 (solid) compared with 305/40R19 (dashed outline), drawn to scale

With 305/40R19 tires, when your speedometer says 60 mph you are really going

62.6 mph

305/40R19 is +1.20 inches (+4.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/35R19305/40R19Difference%
Overall diameter27.41"28.61"+1.20"+4.4%
Section width12.01"12.01"0.00"0.0%
Sidewall height4.20"4.80"+0.60"+14.3%
Circumference86.10"89.87"+3.77"+4.4%
Revolutions per mile735.9705.0−30.9−4.2%

Speedometer difference

If your vehicle came with 305/35R19 and you fit 305/40R19, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.8 mph+1.8 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.1 mph+3.1 mph
75 mph78.3 mph+3.3 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 305/35R19 or 305/40R19?
305/40R19 is taller by 1.20 inches (28.61" vs 27.41"). 305/35R19 is the same width.
Can I replace 305/35R19 with 305/40R19?
It is not recommended without checking carefully. The diameter difference is +4.4%, 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 305/40R19 change my speedometer?
When your speedometer reads 60 mph with 305/40R19 fitted (calibrated for 305/35R19), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.4%.
Will 305/40R19 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

Other comparisons