Tire Size Box

185/55R15 vs 225/40R16

225/40R16 compared with 185/55R15

+0.3% diameter, +1.6" width

225/40R16 is 23.09" tall vs 23.01". Within the 3% rule, so usually interchangeable.

23.0"15" rim4.0"7.3" wide
185/55R15 (solid) compared with 225/40R16 (dashed outline), drawn to scale

With 225/40R16 tires, when your speedometer says 60 mph you are really going

60.2 mph

225/40R16 is +0.07 inches (+0.3%) in overall diameter. That is within the 3% most shops and makers allow.

185/55R15225/40R16Difference%
Overall diameter23.01"23.09"+0.07"+0.3%
Section width7.28"8.86"+1.57"+21.6%
Sidewall height4.01"3.54"−0.46"−11.5%
Circumference72.29"72.53"+0.24"+0.3%
Revolutions per mile876.4873.6−2.8−0.3%

Speedometer difference

If your vehicle came with 185/55R15 and you fit 225/40R16, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.1 mph+0.1 mph
30 mph30.1 mph+0.1 mph
40 mph40.1 mph+0.1 mph
50 mph50.2 mph+0.2 mph
60 mph60.2 mph+0.2 mph
65 mph65.2 mph+0.2 mph
70 mph70.2 mph+0.2 mph
75 mph75.2 mph+0.2 mph
80 mph80.3 mph+0.3 mph

Each size on its own

Questions

Which is bigger, 185/55R15 or 225/40R16?
225/40R16 is taller by 0.07 inches (23.09" vs 23.01"). 225/40R16 is wider by 1.57 inches.
Can I replace 185/55R15 with 225/40R16?
Usually, yes. The diameter difference is +0.3%, 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 225/40R16 change my speedometer?
When your speedometer reads 60 mph with 225/40R16 fitted (calibrated for 185/55R15), your real speed is 60.2 mph. Your odometer will under-count miles by about 0.3%.
Will 225/40R16 lift my vehicle?
Ride height changes by half the diameter difference: +0.04 inches of ground clearance at the axle.

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