Tire Size Box

185/65R17 vs 215/50R18

215/50R18 compared with 185/65R17

0.0% diameter, +1.2" width

215/50R18 is 26.46" tall vs 26.47". Within the 3% rule, so usually interchangeable.

26.5"17" rim4.7"7.3" wide
185/65R17 (solid) compared with 215/50R18 (dashed outline), drawn to scale

With 215/50R18 tires, when your speedometer says 60 mph you are really going

60.0 mph

215/50R18 is 0.00 inches (0.0%) in overall diameter. That is within the 3% most shops and makers allow.

185/65R17215/50R18Difference%
Overall diameter26.47"26.46"0.00"0.0%
Section width7.28"8.46"+1.18"+16.2%
Sidewall height4.73"4.23"−0.50"−10.6%
Circumference83.15"83.14"−0.01"0.0%
Revolutions per mile762.0762.1+0.10.0%

Speedometer difference

If your vehicle came with 185/65R17 and you fit 215/50R18, 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, 185/65R17 or 215/50R18?
They are the same overall diameter, 26.47 inches.
Can I replace 185/65R17 with 215/50R18?
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 215/50R18 change my speedometer?
When your speedometer reads 60 mph with 215/50R18 fitted (calibrated for 185/65R17), your real speed is 60.0 mph. Your odometer will over-count miles by about 0.0%.
Will 215/50R18 lift my vehicle?
Ride height changes by half the diameter difference: 0.00 inches of ground clearance at the axle.

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