Tire Size Box

305/45R17 vs 305/55R17

305/55R17 compared with 305/45R17

+8.6% diameter, 0.0" width

305/55R17 is 30.21" tall vs 27.81". More than the 3% rule of thumb, so check carefully before switching.

27.8"17" rim5.4"12.0" wide
305/45R17 (solid) compared with 305/55R17 (dashed outline), drawn to scale

With 305/55R17 tires, when your speedometer says 60 mph you are really going

65.2 mph

305/55R17 is +2.40 inches (+8.6%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/45R17305/55R17Difference%
Overall diameter27.81"30.21"+2.40"+8.6%
Section width12.01"12.01"0.00"0.0%
Sidewall height5.40"6.60"+1.20"+22.2%
Circumference87.36"94.90"+7.54"+8.6%
Revolutions per mile725.3667.6−57.7−7.9%

Speedometer difference

If your vehicle came with 305/45R17 and you fit 305/55R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.7 mph+1.7 mph
30 mph32.6 mph+2.6 mph
40 mph43.5 mph+3.5 mph
50 mph54.3 mph+4.3 mph
60 mph65.2 mph+5.2 mph
65 mph70.6 mph+5.6 mph
70 mph76.0 mph+6.0 mph
75 mph81.5 mph+6.5 mph
80 mph86.9 mph+6.9 mph

Each size on its own

Questions

Which is bigger, 305/45R17 or 305/55R17?
305/55R17 is taller by 2.40 inches (30.21" vs 27.81"). 305/45R17 is the same width.
Can I replace 305/45R17 with 305/55R17?
It is not recommended without checking carefully. The diameter difference is +8.6%, 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 305/55R17 change my speedometer?
When your speedometer reads 60 mph with 305/55R17 fitted (calibrated for 305/45R17), your real speed is 65.2 mph. Your odometer will under-count miles by about 8.6%.
Will 305/55R17 lift my vehicle?
Ride height changes by half the diameter difference: +1.20 inches of ground clearance at the axle.

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