Tire Size Box

285/60R17 vs 305/60R17

305/60R17 compared with 285/60R17

+3.1% diameter, +0.8" width

305/60R17 is 31.41" tall vs 30.46". More than the 3% rule of thumb, so check carefully before switching.

30.5"17" rim6.7"11.2" wide
285/60R17 (solid) compared with 305/60R17 (dashed outline), drawn to scale

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

61.9 mph

305/60R17 is +0.94 inches (+3.1%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/60R17305/60R17Difference%
Overall diameter30.46"31.41"+0.94"+3.1%
Section width11.22"12.01"+0.79"+7.0%
Sidewall height6.73"7.20"+0.47"+7.0%
Circumference95.71"98.68"+2.97"+3.1%
Revolutions per mile662.0642.1−19.9−3.0%

Speedometer difference

If your vehicle came with 285/60R17 and you fit 305/60R17, 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 mph51.6 mph+1.6 mph
60 mph61.9 mph+1.9 mph
65 mph67.0 mph+2.0 mph
70 mph72.2 mph+2.2 mph
75 mph77.3 mph+2.3 mph
80 mph82.5 mph+2.5 mph

Each size on its own

Questions

Which is bigger, 285/60R17 or 305/60R17?
305/60R17 is taller by 0.94 inches (31.41" vs 30.46"). 305/60R17 is wider by 0.79 inches.
Can I replace 285/60R17 with 305/60R17?
It is not recommended without checking carefully. The diameter difference is +3.1%, 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 305/60R17 change my speedometer?
When your speedometer reads 60 mph with 305/60R17 fitted (calibrated for 285/60R17), your real speed is 61.9 mph. Your odometer will under-count miles by about 3.1%.
Will 305/60R17 lift my vehicle?
Ride height changes by half the diameter difference: +0.47 inches of ground clearance at the axle.

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