Is 285/60R20 bigger than 285/55R20?

285/60R20 is 1.12 inches taller and 0 mm wider. In overall diameter that is +3.47%, which exceeds the ±3% rule of thumb for a substitution.

How much will 285/60R20 throw off my speedometer?

Every reading scales by 1.03469. An indicated 60 mph becomes 62.1 mph, and every 100 miles on the odometer is really 103.5 miles.

How much does 285/60R20 change ground clearance over 285/55R20?

The axle centerline moves by 0.56 inches — half the diameter change, because half the extra height sits below the hub and half above it.

Will 285/60R20 fit where 285/55R20 fits?

Nothing derived from the size code can answer that. Clearance depends on wheel offset, suspension travel and body dimensions that no tire size contains. This page tells you exactly what changes dimensionally, which is the part that can be calculated.

285/55R20 vs 285/60R20

285/60R20 is +1.12″ in overall diameter and 0 mm in section width against 285/55R20 — a diameter change of +3.47%, which breaks the ±3% substitution rule. An indicated 60 mph would really be 62.1 mph.

Outside 3%

Every dimension

Difference between 285/55R20 and 285/60R20
Dimension	285/55R20 → 285/60R20	Change
Overall diameter	32.34″ → 33.46″	+1.12″ (+3.47%)
Section width	285 mm → 285 mm	0 mm (0.00%)
Sidewall height	156.8 mm → 171.0 mm	+14.3 mm
Rolling circumference	101.61″ → 105.13″	+3.53″
Revolutions per mile	623.6 → 602.7	−20.9
Axle height / clearance	16.17″ → 16.73″	+0.56″

285/55R20285 mm

285/60R20285 mm

285/55R20 32.34″285/60R20 33.46″

Which is taller, 285/55R20 or 285/60R20?

285/60R20 is the taller of the two, at 33.46″ against 32.34″. The gap is 1.12 inches, or 28.5 mm.

Both are metric sizes, so neither states its height directly. Both figures below are derived from the section width, aspect ratio and wheel diameter in the code. 285/55R20 is 285 mm wide with a 156.8 mm sidewall on a 20″ wheel; 285/60R20 is 285 mm wide with a 171.0 mm sidewall on a 20″ wheel.

What the speedometer will read

Indicated versus actual speed after the size change
Speedometer reads	Actual speed	Error
25 mph	25.9 mph	+0.9 mph
40 mph	41.4 mph	+1.4 mph
55 mph	56.9 mph	+1.9 mph
60 mph	62.1 mph	+2.1 mph
70 mph	72.4 mph	+2.4 mph
80 mph	82.8 mph	+2.8 mph

Fitting 285/60R20 in place of 285/55R20 multiplies every speed and distance reading by 1.03469. Over 10,000 indicated miles the odometer is out by +347 miles.

Effective gearing moves by the same proportion. A vehicle with 3.73 axles running 285/55R20 would need 3.86 to keep the same engine speed on 285/60R20. Work it out for your own axle ratio.

Full specification of each size

285/55R20

Derived dimensions for 285/55R20
Dimension	Metric	Imperial
Section width	285.0 mm	11.22″
Sidewall height	156.8 mm	6.17″
Wheel diameter	508.0 mm	20.0″
Overall diameter	821.5 mm	32.34″
Rolling circumference	2,580.8 mm	101.61″
Revolutions per mile	387.5 / km	623.6 / mile
Measuring rim (estimate)	229 mm	9″

285/60R20

Derived dimensions for 285/60R20
Dimension	Metric	Imperial
Section width	285.0 mm	11.22″
Sidewall height	171.0 mm	6.73″
Wheel diameter	508.0 mm	20.0″
Overall diameter	850.0 mm	33.46″
Rolling circumference	2,670.4 mm	105.13″
Revolutions per mile	374.5 / km	602.7 / mile
Measuring rim (estimate)	229 mm	9″

Rim widths differ too: 285/55R20 is designed for 8.5″–10″ and 285/60R20 for 8.5″–10″. They share a measuring rim, so one wheel can usually carry either.

Can you swap one for the other?

Outside the ±3% rule

The diameter difference of +3.47% exceeds the ±3% rule of thumb. Expect a speedometer error of about 2.1 mph at an indicated 60, and an odometer that is off by the same proportion. It is a common swap even so — it just needs the instruments recalibrated to stay honest.

Neither figure says anything about physical fitment. Whether 285/60R20 clears the strut, the fender liner and the steering stops depends on wheel offset and suspension geometry that a size code does not encode. For maintenance rather than sizing, Car Basics covers tire care.