Tire Size Box

215/40R16 vs 185/40R17

185/40R17 compared with 215/40R16

+0.2% diameter, −1.2" width

185/40R17 is 22.83" tall vs 22.77". Within the 3% rule, so usually interchangeable.

22.8"16" rim3.4"8.5" wide
215/40R16 (solid) compared with 185/40R17 (dashed outline), drawn to scale

With 185/40R17 tires, when your speedometer says 60 mph you are really going

60.1 mph

185/40R17 is +0.06 inches (+0.2%) in overall diameter. That is within the 3% most shops and makers allow.

215/40R16185/40R17Difference%
Overall diameter22.77"22.83"+0.06"+0.2%
Section width8.46"7.28"−1.18"−14.0%
Sidewall height3.39"2.91"−0.47"−14.0%
Circumference71.54"71.71"+0.17"+0.2%
Revolutions per mile885.7883.5−2.1−0.2%

Speedometer difference

If your vehicle came with 215/40R16 and you fit 185/40R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.0 mph0.0 mph
30 mph30.1 mph+0.1 mph
40 mph40.1 mph+0.1 mph
50 mph50.1 mph+0.1 mph
60 mph60.1 mph+0.1 mph
65 mph65.2 mph+0.2 mph
70 mph70.2 mph+0.2 mph
75 mph75.2 mph+0.2 mph
80 mph80.2 mph+0.2 mph

Each size on its own

Questions

Which is bigger, 215/40R16 or 185/40R17?
185/40R17 is taller by 0.06 inches (22.83" vs 22.77"). 215/40R16 is wider by 1.18 inches.
Can I replace 215/40R16 with 185/40R17?
Usually, yes. The diameter difference is +0.2%, 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 185/40R17 change my speedometer?
When your speedometer reads 60 mph with 185/40R17 fitted (calibrated for 215/40R16), your real speed is 60.1 mph. Your odometer will under-count miles by about 0.2%.
Will 185/40R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.03 inches of ground clearance at the axle.

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