Tire Size Box

195/45R18 vs 195/55R18

195/55R18 compared with 195/45R18

+6.2% diameter, 0.0" width

195/55R18 is 26.44" 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 195/55R18 (dashed outline), drawn to scale

With 195/55R18 tires, when your speedometer says 60 mph you are really going

63.7 mph

195/55R18 is +1.54 inches (+6.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

195/45R18195/55R18Difference%
Overall diameter24.91"26.44"+1.54"+6.2%
Section width7.68"7.68"0.00"0.0%
Sidewall height3.45"4.22"+0.77"+22.2%
Circumference78.26"83.08"+4.82"+6.2%
Revolutions per mile809.7762.6−47.0−5.8%

Speedometer difference

If your vehicle came with 195/45R18 and you fit 195/55R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.2 mph+1.2 mph
30 mph31.8 mph+1.8 mph
40 mph42.5 mph+2.5 mph
50 mph53.1 mph+3.1 mph
60 mph63.7 mph+3.7 mph
65 mph69.0 mph+4.0 mph
70 mph74.3 mph+4.3 mph
75 mph79.6 mph+4.6 mph
80 mph84.9 mph+4.9 mph

Each size on its own

Questions

Which is bigger, 195/45R18 or 195/55R18?
195/55R18 is taller by 1.54 inches (26.44" vs 24.91"). 195/45R18 is the same width.
Can I replace 195/45R18 with 195/55R18?
It is not recommended without checking carefully. The diameter difference is +6.2%, 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 195/55R18 change my speedometer?
When your speedometer reads 60 mph with 195/55R18 fitted (calibrated for 195/45R18), your real speed is 63.7 mph. Your odometer will under-count miles by about 6.2%.
Will 195/55R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.77 inches of ground clearance at the axle.

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