Tire Size Box

175/55R16 vs 185/45R17

185/45R17 compared with 175/55R16

−0.1% diameter, +0.4" width

185/45R17 is 23.56" tall vs 23.58". Within the 3% rule, so usually interchangeable.

23.6"16" rim3.8"6.9" wide
175/55R16 (solid) compared with 185/45R17 (dashed outline), drawn to scale

With 185/45R17 tires, when your speedometer says 60 mph you are really going

59.9 mph

185/45R17 is −0.02 inches (−0.1%) in overall diameter. That is within the 3% most shops and makers allow.

175/55R16185/45R17Difference%
Overall diameter23.58"23.56"−0.02"−0.1%
Section width6.89"7.28"+0.39"+5.7%
Sidewall height3.79"3.28"−0.51"−13.5%
Circumference74.07"74.00"−0.07"−0.1%
Revolutions per mile855.4856.2+0.9+0.1%

Speedometer difference

If your vehicle came with 175/55R16 and you fit 185/45R17, 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 mph49.9 mph−0.1 mph
60 mph59.9 mph−0.1 mph
65 mph64.9 mph−0.1 mph
70 mph69.9 mph−0.1 mph
75 mph74.9 mph−0.1 mph
80 mph79.9 mph−0.1 mph

Each size on its own

Questions

Which is bigger, 175/55R16 or 185/45R17?
175/55R16 is taller by 0.02 inches (23.58" vs 23.56"). 185/45R17 is wider by 0.39 inches.
Can I replace 175/55R16 with 185/45R17?
Usually, yes. The diameter difference is −0.1%, 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 185/45R17 change my speedometer?
When your speedometer reads 60 mph with 185/45R17 fitted (calibrated for 175/55R16), your real speed is 59.9 mph. Your odometer will over-count miles by about 0.1%.
Will 185/45R17 lift my vehicle?
Ride height changes by half the diameter difference: −0.01 inches of ground clearance at the axle.

Other comparisons