Tire Size Box

40x13.50R20 vs 40x15.50R20

40x15.50R20 compared with 40x13.50R20

0.0% diameter, +2.0" width

40x15.50R20 is 40.00" tall vs 40.00". Within the 3% rule, so usually interchangeable.

40.0"20" rim10.0"13.5" wide
40x13.50R20 (solid) compared with 40x15.50R20 (dashed outline), drawn to scale

With 40x15.50R20 tires, when your speedometer says 60 mph you are really going

60.0 mph

40x15.50R20 is 0.00 inches (0.0%) in overall diameter. That is within the 3% most shops and makers allow.

40x13.50R2040x15.50R20Difference%
Overall diameter40.00"40.00"0.00"0.0%
Section width13.50"15.50"+2.00"+14.8%
Sidewall height10.00"10.00"0.00"0.0%
Circumference125.66"125.66"0.00"0.0%
Revolutions per mile504.2504.20.00.0%

Speedometer difference

If your vehicle came with 40x13.50R20 and you fit 40x15.50R20, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.0 mph0.0 mph
30 mph30.0 mph0.0 mph
40 mph40.0 mph0.0 mph
50 mph50.0 mph0.0 mph
60 mph60.0 mph0.0 mph
65 mph65.0 mph0.0 mph
70 mph70.0 mph0.0 mph
75 mph75.0 mph0.0 mph
80 mph80.0 mph0.0 mph

Each size on its own

Questions

Which is bigger, 40x13.50R20 or 40x15.50R20?
They are the same overall diameter, 40.00 inches.
Can I replace 40x13.50R20 with 40x15.50R20?
Usually, yes. The diameter difference is 0.0%, inside the 3% rule of thumb most tire shops use. Check that the wider or taller tire clears your suspension and fenders, and that its load index meets your placard.
How much will 40x15.50R20 change my speedometer?
When your speedometer reads 60 mph with 40x15.50R20 fitted (calibrated for 40x13.50R20), your real speed is 60.0 mph. Your odometer will under-count miles by about 0.0%.
Will 40x15.50R20 lift my vehicle?
Ride height changes by half the diameter difference: 0.00 inches of ground clearance at the axle.