Tire Size Box

215/45R18 vs 215/55R18

215/55R18 compared with 215/45R18

+6.6% diameter, 0.0" width

215/55R18 is 27.31" tall vs 25.62". More than the 3% rule of thumb, so check carefully before switching.

25.6"18" rim3.8"8.5" wide
215/45R18 (solid) compared with 215/55R18 (dashed outline), drawn to scale

With 215/55R18 tires, when your speedometer says 60 mph you are really going

64.0 mph

215/55R18 is +1.69 inches (+6.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

215/45R18215/55R18Difference%
Overall diameter25.62"27.31"+1.69"+6.6%
Section width8.46"8.46"0.00"0.0%
Sidewall height3.81"4.66"+0.85"+22.2%
Circumference80.48"85.80"+5.32"+6.6%
Revolutions per mile787.3738.5−48.8−6.2%

Speedometer difference

If your vehicle came with 215/45R18 and you fit 215/55R18, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.3 mph+1.3 mph
30 mph32.0 mph+2.0 mph
40 mph42.6 mph+2.6 mph
50 mph53.3 mph+3.3 mph
60 mph64.0 mph+4.0 mph
65 mph69.3 mph+4.3 mph
70 mph74.6 mph+4.6 mph
75 mph80.0 mph+5.0 mph
80 mph85.3 mph+5.3 mph

Each size on its own

Questions

Which is bigger, 215/45R18 or 215/55R18?
215/55R18 is taller by 1.69 inches (27.31" vs 25.62"). 215/45R18 is the same width.
Can I replace 215/45R18 with 215/55R18?
It is not recommended without checking carefully. The diameter difference is +6.6%, 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 215/55R18 change my speedometer?
When your speedometer reads 60 mph with 215/55R18 fitted (calibrated for 215/45R18), your real speed is 64.0 mph. Your odometer will under-count miles by about 6.6%.
Will 215/55R18 lift my vehicle?
Ride height changes by half the diameter difference: +0.85 inches of ground clearance at the axle.

Other comparisons