Tire Size Box

305/45R17 vs 305/50R17

305/50R17 compared with 305/45R17

+4.3% diameter, 0.0" width

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

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

62.6 mph

305/50R17 is +1.20 inches (+4.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

305/45R17305/50R17Difference%
Overall diameter27.81"29.01"+1.20"+4.3%
Section width12.01"12.01"0.00"0.0%
Sidewall height5.40"6.00"+0.60"+11.1%
Circumference87.36"91.13"+3.77"+4.3%
Revolutions per mile725.3695.3−30.0−4.1%

Speedometer difference

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

Speedometer showsActual speedDifference
20 mph20.9 mph+0.9 mph
30 mph31.3 mph+1.3 mph
40 mph41.7 mph+1.7 mph
50 mph52.2 mph+2.2 mph
60 mph62.6 mph+2.6 mph
65 mph67.8 mph+2.8 mph
70 mph73.0 mph+3.0 mph
75 mph78.2 mph+3.2 mph
80 mph83.5 mph+3.5 mph

Each size on its own

Questions

Which is bigger, 305/45R17 or 305/50R17?
305/50R17 is taller by 1.20 inches (29.01" vs 27.81"). 305/45R17 is the same width.
Can I replace 305/45R17 with 305/50R17?
It is not recommended without checking carefully. The diameter difference is +4.3%, 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 305/50R17 change my speedometer?
When your speedometer reads 60 mph with 305/50R17 fitted (calibrated for 305/45R17), your real speed is 62.6 mph. Your odometer will under-count miles by about 4.3%.
Will 305/50R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.60 inches of ground clearance at the axle.

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