Tire Size Box

195/40R18 vs 195/50R18

195/50R18 compared with 195/40R18

+6.4% diameter, 0.0" width

195/50R18 is 25.68" tall vs 24.14". More than the 3% rule of thumb, so check carefully before switching.

24.1"18" rim3.1"7.7" wide
195/40R18 (solid) compared with 195/50R18 (dashed outline), drawn to scale

With 195/50R18 tires, when your speedometer says 60 mph you are really going

63.8 mph

195/50R18 is +1.54 inches (+6.4%) in overall diameter. That is more than the 3% most shops and makers recommend.

195/40R18195/50R18Difference%
Overall diameter24.14"25.68"+1.54"+6.4%
Section width7.68"7.68"0.00"0.0%
Sidewall height3.07"3.84"+0.77"+25.0%
Circumference75.84"80.67"+4.82"+6.4%
Revolutions per mile835.4785.4−50.0−6.0%

Speedometer difference

If your vehicle came with 195/40R18 and you fit 195/50R18, 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 mph42.5 mph+2.5 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, 195/40R18 or 195/50R18?
195/50R18 is taller by 1.54 inches (25.68" vs 24.14"). 195/40R18 is the same width.
Can I replace 195/40R18 with 195/50R18?
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 195/50R18 change my speedometer?
When your speedometer reads 60 mph with 195/50R18 fitted (calibrated for 195/40R18), your real speed is 63.8 mph. Your odometer will under-count miles by about 6.4%.
Will 195/50R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.77 inches of ground clearance at the axle.

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