Tire Size Box

185/45R16 vs 185/55R16

185/55R16 compared with 185/45R16

+6.5% diameter, 0.0" width

185/55R16 is 24.01" tall vs 22.56". More than the 3% rule of thumb, so check carefully before switching.

22.6"16" rim3.3"7.3" wide
185/45R16 (solid) compared with 185/55R16 (dashed outline), drawn to scale

With 185/55R16 tires, when your speedometer says 60 mph you are really going

63.9 mph

185/55R16 is +1.46 inches (+6.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

185/45R16185/55R16Difference%
Overall diameter22.56"24.01"+1.46"+6.5%
Section width7.28"7.28"0.00"0.0%
Sidewall height3.28"4.01"+0.73"+22.2%
Circumference70.86"75.44"+4.58"+6.5%
Revolutions per mile894.2839.9−54.2−6.1%

Speedometer difference

If your vehicle came with 185/45R16 and you fit 185/55R16, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph31.9 mph+1.9 mph
40 mph42.6 mph+2.6 mph
50 mph53.2 mph+3.2 mph
60 mph63.9 mph+3.9 mph
65 mph69.2 mph+4.2 mph
70 mph74.5 mph+4.5 mph
75 mph79.8 mph+4.8 mph
80 mph85.2 mph+5.2 mph

Each size on its own

Questions

Which is bigger, 185/45R16 or 185/55R16?
185/55R16 is taller by 1.46 inches (24.01" vs 22.56"). 185/45R16 is the same width.
Can I replace 185/45R16 with 185/55R16?
It is not recommended without checking carefully. The diameter difference is +6.5%, 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 185/55R16 change my speedometer?
When your speedometer reads 60 mph with 185/55R16 fitted (calibrated for 185/45R16), your real speed is 63.9 mph. Your odometer will under-count miles by about 6.5%.
Will 185/55R16 lift my vehicle?
Ride height changes by half the diameter difference: +0.73 inches of ground clearance at the axle.

Other comparisons