Tire Size Box

235/45R17 vs 235/55R17

235/55R17 compared with 235/45R17

+7.3% diameter, 0.0" width

235/55R17 is 27.18" tall vs 25.33". More than the 3% rule of thumb, so check carefully before switching.

25.3"17" rim4.2"9.3" wide
235/45R17 (solid) compared with 235/55R17 (dashed outline), drawn to scale

With 235/55R17 tires, when your speedometer says 60 mph you are really going

64.4 mph

235/55R17 is +1.85 inches (+7.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

235/45R17235/55R17Difference%
Overall diameter25.33"27.18"+1.85"+7.3%
Section width9.25"9.25"0.00"0.0%
Sidewall height4.16"5.09"+0.93"+22.2%
Circumference79.57"85.38"+5.81"+7.3%
Revolutions per mile796.3742.1−54.2−6.8%

Speedometer difference

If your vehicle came with 235/45R17 and you fit 235/55R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.2 mph+2.2 mph
40 mph42.9 mph+2.9 mph
50 mph53.7 mph+3.7 mph
60 mph64.4 mph+4.4 mph
65 mph69.7 mph+4.7 mph
70 mph75.1 mph+5.1 mph
75 mph80.5 mph+5.5 mph
80 mph85.8 mph+5.8 mph

Each size on its own

Questions

Which is bigger, 235/45R17 or 235/55R17?
235/55R17 is taller by 1.85 inches (27.18" vs 25.33"). 235/45R17 is the same width.
Can I replace 235/45R17 with 235/55R17?
It is not recommended without checking carefully. The diameter difference is +7.3%, 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 235/55R17 change my speedometer?
When your speedometer reads 60 mph with 235/55R17 fitted (calibrated for 235/45R17), your real speed is 64.4 mph. Your odometer will under-count miles by about 7.3%.
Will 235/55R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.93 inches of ground clearance at the axle.

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