Tire Size Box

285/65R17 vs 305/65R17

305/65R17 compared with 285/65R17

+3.2% diameter, +0.8" width

305/65R17 is 32.61" tall vs 31.59". More than the 3% rule of thumb, so check carefully before switching.

31.6"17" rim7.3"11.2" wide
285/65R17 (solid) compared with 305/65R17 (dashed outline), drawn to scale

With 305/65R17 tires, when your speedometer says 60 mph you are really going

61.9 mph

305/65R17 is +1.02 inches (+3.2%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/65R17305/65R17Difference%
Overall diameter31.59"32.61"+1.02"+3.2%
Section width11.22"12.01"+0.79"+7.0%
Sidewall height7.29"7.81"+0.51"+7.0%
Circumference99.23"102.45"+3.22"+3.2%
Revolutions per mile638.5618.5−20.0−3.1%

Speedometer difference

If your vehicle came with 285/65R17 and you fit 305/65R17, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph20.6 mph+0.6 mph
30 mph31.0 mph+1.0 mph
40 mph41.3 mph+1.3 mph
50 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.1 mph+2.1 mph
70 mph72.3 mph+2.3 mph
75 mph77.4 mph+2.4 mph
80 mph82.6 mph+2.6 mph

Each size on its own

Questions

Which is bigger, 285/65R17 or 305/65R17?
305/65R17 is taller by 1.02 inches (32.61" vs 31.59"). 305/65R17 is wider by 0.79 inches.
Can I replace 285/65R17 with 305/65R17?
It is not recommended without checking carefully. The diameter difference is +3.2%, 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 305/65R17 change my speedometer?
When your speedometer reads 60 mph with 305/65R17 fitted (calibrated for 285/65R17), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.2%.
Will 305/65R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.51 inches of ground clearance at the axle.

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