Tire Size Box

185/40R17 vs 185/50R17

185/50R17 compared with 185/40R17

+6.4% diameter, 0.0" width

185/50R17 is 24.28" tall vs 22.83". More than the 3% rule of thumb, so check carefully before switching.

22.8"17" rim2.9"7.3" wide
185/40R17 (solid) compared with 185/50R17 (dashed outline), drawn to scale

With 185/50R17 tires, when your speedometer says 60 mph you are really going

63.8 mph

185/50R17 is +1.46 inches (+6.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

185/40R17185/50R17Difference%
Overall diameter22.83"24.28"+1.46"+6.4%
Section width7.28"7.28"0.00"0.0%
Sidewall height2.91"3.64"+0.73"+25.0%
Circumference71.71"76.29"+4.58"+6.4%
Revolutions per mile883.5830.5−53.0−6.0%

Speedometer difference

If your vehicle came with 185/40R17 and you fit 185/50R17, 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 mph63.8 mph+3.8 mph
65 mph69.1 mph+4.1 mph
70 mph74.5 mph+4.5 mph
75 mph79.8 mph+4.8 mph
80 mph85.1 mph+5.1 mph

Each size on its own

Questions

Which is bigger, 185/40R17 or 185/50R17?
185/50R17 is taller by 1.46 inches (24.28" vs 22.83"). 185/40R17 is the same width.
Can I replace 185/40R17 with 185/50R17?
It is not recommended without checking carefully. The diameter difference is +6.4%, 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 185/50R17 change my speedometer?
When your speedometer reads 60 mph with 185/50R17 fitted (calibrated for 185/40R17), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.4%.
Will 185/50R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.73 inches of ground clearance at the axle.

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