Tire Size Box

285/75R17 vs 305/75R17

305/75R17 compared with 285/75R17

+3.5% diameter, +0.8" width

305/75R17 is 35.01" tall vs 33.83". More than the 3% rule of thumb, so check carefully before switching.

33.8"17" rim8.4"11.2" wide
285/75R17 (solid) compared with 305/75R17 (dashed outline), drawn to scale

With 305/75R17 tires, when your speedometer says 60 mph you are really going

62.1 mph

305/75R17 is +1.18 inches (+3.5%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/75R17305/75R17Difference%
Overall diameter33.83"35.01"+1.18"+3.5%
Section width11.22"12.01"+0.79"+7.0%
Sidewall height8.42"9.01"+0.59"+7.0%
Circumference106.28"109.99"+3.71"+3.5%
Revolutions per mile596.1576.0−20.1−3.4%

Speedometer difference

If your vehicle came with 285/75R17 and you fit 305/75R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.7 mph+0.7 mph
30 mph31.0 mph+1.0 mph
40 mph41.4 mph+1.4 mph
50 mph51.7 mph+1.7 mph
60 mph62.1 mph+2.1 mph
65 mph67.3 mph+2.3 mph
70 mph72.4 mph+2.4 mph
75 mph77.6 mph+2.6 mph
80 mph82.8 mph+2.8 mph

Each size on its own

Questions

Which is bigger, 285/75R17 or 305/75R17?
305/75R17 is taller by 1.18 inches (35.01" vs 33.83"). 305/75R17 is wider by 0.79 inches.
Can I replace 285/75R17 with 305/75R17?
It is not recommended without checking carefully. The diameter difference is +3.5%, 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 305/75R17 change my speedometer?
When your speedometer reads 60 mph with 305/75R17 fitted (calibrated for 285/75R17), your real speed is 62.1 mph. Your odometer will under-count miles by about 3.5%.
Will 305/75R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.59 inches of ground clearance at the axle.

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