TruckTally

285/45R20 tire size

285mm wide with a 45% aspect ratio on a 20-inch wheel — 30.1 inches tall overall. Below: what it measures, what it swaps with, and which trucks run it from the factory.

Overall diameter
30.10"
Section width
11.22"
285mm
Sidewall height
5.05"
Revs per mile
670
94.6" circumference

Sizes that swap with 285/45R20

Within 3% of the original diameter — close enough to fit without a recalibration or clearance work on most trucks.

SizeDiameterDifferenceWidth
255/70R1630.06"-0.04" (-0.1%)10.0"
255/55R1930.04"-0.06" (-0.2%)10.0"
255/50R2030.04"-0.06" (-0.2%)10.0"
265/50R2030.43"+0.33" (+1.1%)10.4"
245/75R1630.47"+0.37" (+1.2%)9.6"
245/70R1730.50"+0.41" (+1.3%)9.6"
265/60R1830.52"+0.42" (+1.4%)10.4"
245/50R2029.65"-0.45" (-1.5%)9.6"

Plus and minus sizing

Same overall height on a different wheel. Going down a wheel size buys sidewall for off-road; going up is usually about looks. Gearing and speedometer stay put either way.

Compare 285/45R20 against your current size

Tire size comparison

Diameter change, speedometer error, and whether it will rub.

Current / stock size

30.1" tall · 11.2" wide ·

New size

30.1" tall · 10.0" wide ·

Direct fit

Diameter and width are close enough to stock that this is a bolt-on swap on an unmodified truck.

20"30.1" tall285/45R2016"30.1" tall255/70R1611.2" wide10.0" wide
Drawn to scale from the calculated sizes. Circles compare overall height and wheel diameter; the bars underneath compare section width.
Diameter change
-0.04"
-0.1% — 30.10" to 30.06"
Speedometer at 70
69.9mph actual
Reads 0.1% fast — you are going slower than it says.
Ride height
-0.02"
Change at the axle, before any lift or leveling kit.
Section width
-1.18"
11.22" to 10.04"
Revs per mile
671
+1 vs. stock (670)
Odometer drift
999real miles
Actual distance covered per 1,000 miles shown on the odometer.
  • Within the range normally treated as a direct swap — no clearance work expected.

Reading this size

285/45R20 breaks down as 285mm section width, an aspect ratio of 45 (the sidewall is 45% of the width, so 5.05 inches), and a 20-inch wheel. Overall diameter is the wheel plus two sidewalls: 20 + 5.05 + 5.05 = 30.10 inches.

That last figure is the one that matters when you change size. The speedometer, odometer, transmission shift points and stability control all assume the factory diameter, so staying within a few percent keeps everything calibrated. Width matters for clearance rather than gearing — it decides whether the tire touches the suspension at full lock.

Common questions

How tall is a 285/45R20 tire?

30.10 inches in overall diameter, with a 5.05-inch sidewall on a 20-inch wheel. Section width is 11.22 inches (285mm), and it turns about 670 times per mile. Real tires vary from the nominal figure by up to half an inch depending on brand and tread.

What is equivalent to a 285/45R20?

The closest common size is 255/70R16 at 30.06 inches — -0.1% different. Anything within about 3% of the original diameter swaps on without upsetting the speedometer badly or needing a tune.

Will 285/45R20 fit my truck?

We do not have it listed as a factory size on the trucks we cover, so treat it as an upgrade size. Put your current size into the calculator on this page to see the diameter change and whether it is likely to rub.

Does going to 285/45R20 affect my speedometer?

Only if the overall diameter changes. The speedometer counts wheel rotations and multiplies by the factory tire circumference, so a larger tire makes the truck travel further per rotation than the gauge assumes and the display reads low. Around 3% is where transmission shift points and stability control calibration start to matter, and most modern trucks can be recalibrated for the new size.

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