Tire Size Box

235/45R15 vs 235/55R15

235/55R15 compared with 235/45R15

+7.9% diameter, 0.0" width

235/55R15 is 25.18" tall vs 23.33". More than the 3% rule of thumb, so check carefully before switching.

23.3"15" rim4.2"9.3" wide
235/45R15 (solid) compared with 235/55R15 (dashed outline), drawn to scale

With 235/55R15 tires, when your speedometer says 60 mph you are really going

64.8 mph

235/55R15 is +1.85 inches (+7.9%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/45R15235/55R15Difference%
Overall diameter23.33"25.18"+1.85"+7.9%
Section width9.25"9.25"0.00"0.0%
Sidewall height4.16"5.09"+0.93"+22.2%
Circumference73.28"79.10"+5.81"+7.9%
Revolutions per mile864.6801.0−63.5−7.3%

Speedometer difference

If your vehicle came with 235/45R15 and you fit 235/55R15, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.6 mph+1.6 mph
30 mph32.4 mph+2.4 mph
40 mph43.2 mph+3.2 mph
50 mph54.0 mph+4.0 mph
60 mph64.8 mph+4.8 mph
65 mph70.2 mph+5.2 mph
70 mph75.6 mph+5.6 mph
75 mph80.9 mph+5.9 mph
80 mph86.3 mph+6.3 mph

Each size on its own

Questions

Which is bigger, 235/45R15 or 235/55R15?
235/55R15 is taller by 1.85 inches (25.18" vs 23.33"). 235/45R15 is the same width.
Can I replace 235/45R15 with 235/55R15?
It is not recommended without checking carefully. The diameter difference is +7.9%, 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 235/55R15 change my speedometer?
When your speedometer reads 60 mph with 235/55R15 fitted (calibrated for 235/45R15), your real speed is 64.8 mph. Your odometer will under-count miles by about 7.9%.
Will 235/55R15 lift my vehicle?
Ride height changes by half the diameter difference: +0.93 inches of ground clearance at the axle.

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