Tire Size Box

195/45R18 vs 195/50R18

195/50R18 compared with 195/45R18

+3.1% diameter, 0.0" width

195/50R18 is 25.68" tall vs 24.91". More than the 3% rule of thumb, so check carefully before switching.

24.9"18" rim3.5"7.7" wide
195/45R18 (solid) compared with 195/50R18 (dashed outline), drawn to scale

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

61.8 mph

195/50R18 is +0.77 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

195/45R18195/50R18Difference%
Overall diameter24.91"25.68"+0.77"+3.1%
Section width7.68"7.68"0.00"0.0%
Sidewall height3.45"3.84"+0.38"+11.1%
Circumference78.26"80.67"+2.41"+3.1%
Revolutions per mile809.7785.4−24.2−3.0%

Speedometer difference

If your vehicle came with 195/45R18 and you fit 195/50R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 195/45R18 or 195/50R18?
195/50R18 is taller by 0.77 inches (25.68" vs 24.91"). 195/45R18 is the same width.
Can I replace 195/45R18 with 195/50R18?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 195/45R18), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.1%.
Will 195/50R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.38 inches of ground clearance at the axle.

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