Tire Size Box

315/45R17 vs 315/55R17

315/55R17 compared with 315/45R17

+8.8% diameter, 0.0" width

315/55R17 is 30.64" tall vs 28.16". More than the 3% rule of thumb, so check carefully before switching.

28.2"17" rim5.6"12.4" wide
315/45R17 (solid) compared with 315/55R17 (dashed outline), drawn to scale

With 315/55R17 tires, when your speedometer says 60 mph you are really going

65.3 mph

315/55R17 is +2.48 inches (+8.8%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/45R17315/55R17Difference%
Overall diameter28.16"30.64"+2.48"+8.8%
Section width12.40"12.40"0.00"0.0%
Sidewall height5.58"6.82"+1.24"+22.2%
Circumference88.47"96.26"+7.79"+8.8%
Revolutions per mile716.2658.2−58.0−8.1%

Speedometer difference

If your vehicle came with 315/45R17 and you fit 315/55R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.8 mph+1.8 mph
30 mph32.6 mph+2.6 mph
40 mph43.5 mph+3.5 mph
50 mph54.4 mph+4.4 mph
60 mph65.3 mph+5.3 mph
65 mph70.7 mph+5.7 mph
70 mph76.2 mph+6.2 mph
75 mph81.6 mph+6.6 mph
80 mph87.0 mph+7.0 mph

Each size on its own

Questions

Which is bigger, 315/45R17 or 315/55R17?
315/55R17 is taller by 2.48 inches (30.64" vs 28.16"). 315/45R17 is the same width.
Can I replace 315/45R17 with 315/55R17?
It is not recommended without checking carefully. The diameter difference is +8.8%, 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 315/55R17 change my speedometer?
When your speedometer reads 60 mph with 315/55R17 fitted (calibrated for 315/45R17), your real speed is 65.3 mph. Your odometer will under-count miles by about 8.8%.
Will 315/55R17 lift my vehicle?
Ride height changes by half the diameter difference: +1.24 inches of ground clearance at the axle.

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