Tire Size Box

285/30R24 vs 285/40R24

285/40R24 compared with 285/30R24

+7.3% diameter, 0.0" width

285/40R24 is 32.98" tall vs 30.73". More than the 3% rule of thumb, so check carefully before switching.

30.7"24" rim3.4"11.2" wide
285/30R24 (solid) compared with 285/40R24 (dashed outline), drawn to scale

With 285/40R24 tires, when your speedometer says 60 mph you are really going

64.4 mph

285/40R24 is +2.24 inches (+7.3%) in overall diameter. That is more than the 3% most shops and makers recommend.

285/30R24285/40R24Difference%
Overall diameter30.73"32.98"+2.24"+7.3%
Section width11.22"11.22"0.00"0.0%
Sidewall height3.37"4.49"+1.12"+33.3%
Circumference96.55"103.60"+7.05"+7.3%
Revolutions per mile656.3611.6−44.7−6.8%

Speedometer difference

If your vehicle came with 285/30R24 and you fit 285/40R24, here is your real speed for each speedometer reading:

Speedometer showsActual speedDifference
20 mph21.5 mph+1.5 mph
30 mph32.2 mph+2.2 mph
40 mph42.9 mph+2.9 mph
50 mph53.7 mph+3.7 mph
60 mph64.4 mph+4.4 mph
65 mph69.7 mph+4.7 mph
70 mph75.1 mph+5.1 mph
75 mph80.5 mph+5.5 mph
80 mph85.8 mph+5.8 mph

Each size on its own

Questions

Which is bigger, 285/30R24 or 285/40R24?
285/40R24 is taller by 2.24 inches (32.98" vs 30.73"). 285/30R24 is the same width.
Can I replace 285/30R24 with 285/40R24?
It is not recommended without checking carefully. The diameter difference is +7.3%, 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 285/40R24 change my speedometer?
When your speedometer reads 60 mph with 285/40R24 fitted (calibrated for 285/30R24), your real speed is 64.4 mph. Your odometer will under-count miles by about 7.3%.
Will 285/40R24 lift my vehicle?
Ride height changes by half the diameter difference: +1.12 inches of ground clearance at the axle.

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