Tire Size Box

315/45R17 vs 305/50R17

305/50R17 compared with 315/45R17

+3.0% diameter, −0.4" width

305/50R17 is 29.01" 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 305/50R17 (dashed outline), drawn to scale

With 305/50R17 tires, when your speedometer says 60 mph you are really going

61.8 mph

305/50R17 is +0.85 inches (+3.0%) in overall diameter. That is more than the 3% most shops and makers recommend.

315/45R17305/50R17Difference%
Overall diameter28.16"29.01"+0.85"+3.0%
Section width12.40"12.01"−0.39"−3.2%
Sidewall height5.58"6.00"+0.42"+7.6%
Circumference88.47"91.13"+2.66"+3.0%
Revolutions per mile716.2695.3−20.9−2.9%

Speedometer difference

If your vehicle came with 315/45R17 and you fit 305/50R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph30.9 mph+0.9 mph
40 mph41.2 mph+1.2 mph
50 mph51.5 mph+1.5 mph
60 mph61.8 mph+1.8 mph
65 mph67.0 mph+2.0 mph
70 mph72.1 mph+2.1 mph
75 mph77.3 mph+2.3 mph
80 mph82.4 mph+2.4 mph

Each size on its own

Questions

Which is bigger, 315/45R17 or 305/50R17?
305/50R17 is taller by 0.85 inches (29.01" vs 28.16"). 315/45R17 is wider by 0.39 inches.
Can I replace 315/45R17 with 305/50R17?
It is not recommended without checking carefully. The diameter difference is +3.0%, 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 305/50R17 change my speedometer?
When your speedometer reads 60 mph with 305/50R17 fitted (calibrated for 315/45R17), your real speed is 61.8 mph. Your odometer will under-count miles by about 3.0%.
Will 305/50R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.42 inches of ground clearance at the axle.

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