Is 205/55R16 bigger than 185/65R15?

205/55R16 is 0.41 inches taller and 20 mm wider. In overall diameter that is +1.67%, which stays inside the ±3% rule of thumb for a substitution.

How much will 205/55R16 throw off my speedometer?

Every reading scales by 1.01673. An indicated 60 mph becomes 61.0 mph, and every 100 miles on the odometer is really 101.7 miles.

How much does 205/55R16 change ground clearance over 185/65R15?

The axle centerline moves by 0.20 inches — half the diameter change, because half the extra height sits below the hub and half above it.

Will 205/55R16 fit where 185/65R15 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.

185/65R15 vs 205/55R16

205/55R16 is +0.41″ in overall diameter and +20 mm in section width against 185/65R15 — a diameter change of +1.67%, which stays inside the ±3% substitution rule. An indicated 60 mph would really be 61.0 mph.

Within 3%

Every dimension

Difference between 185/65R15 and 205/55R16
Dimension	185/65R15 → 205/55R16	Change
Overall diameter	24.47″ → 24.88″	+0.41″ (+1.67%)
Section width	185 mm → 205 mm	+20 mm (+10.81%)
Sidewall height	120.3 mm → 112.8 mm	−7.5 mm
Rolling circumference	76.87″ → 78.16″	+1.29″
Revolutions per mile	824.2 → 810.7	−13.6
Axle height / clearance	12.23″ → 12.44″	+0.20″

185/65R15185 mm

205/55R16205 mm

185/65R15 24.47″205/55R16 24.88″

Which is taller, 185/65R15 or 205/55R16?

205/55R16 is the taller of the two, at 24.88″ against 24.47″. The gap is 0.41 inches, or 10.4 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. 185/65R15 is 185 mm wide with a 120.3 mm sidewall on a 15″ wheel; 205/55R16 is 205 mm wide with a 112.8 mm sidewall on a 16″ wheel.

What the speedometer will read

Indicated versus actual speed after the size change
Speedometer reads	Actual speed	Error
25 mph	25.4 mph	+0.4 mph
40 mph	40.7 mph	+0.7 mph
55 mph	55.9 mph	+0.9 mph
60 mph	61.0 mph	+1.0 mph
70 mph	71.2 mph	+1.2 mph
80 mph	81.3 mph	+1.3 mph

Fitting 205/55R16 in place of 185/65R15 multiplies every speed and distance reading by 1.01673. Over 10,000 indicated miles the odometer is out by +167 miles.

Effective gearing moves by the same proportion. A vehicle with 3.73 axles running 185/65R15 would need 3.79 to keep the same engine speed on 205/55R16. Work it out for your own axle ratio.

Full specification of each size

185/65R15

Derived dimensions for 185/65R15
Dimension	Metric	Imperial
Section width	185.0 mm	7.28″
Sidewall height	120.3 mm	4.73″
Wheel diameter	381.0 mm	15.0″
Overall diameter	621.5 mm	24.47″
Rolling circumference	1,952.5 mm	76.87″
Revolutions per mile	512.2 / km	824.2 / mile
Measuring rim (estimate)	140 mm	5.5″

205/55R16

Derived dimensions for 205/55R16
Dimension	Metric	Imperial
Section width	205.0 mm	8.07″
Sidewall height	112.8 mm	4.44″
Wheel diameter	406.4 mm	16.0″
Overall diameter	631.9 mm	24.88″
Rolling circumference	1,985.2 mm	78.16″
Revolutions per mile	503.7 / km	810.7 / mile
Measuring rim (estimate)	165 mm	6.5″

Rim widths differ too: 185/65R15 is designed for 5″–6.5″ and 205/55R16 for 6″–7.5″. Their measuring rims differ, so the same wheel will not be ideal for both.

Can you swap one for the other?

Inside the ±3% rule

The diameter difference of +1.67% is within the ±3% that fitters use as the boundary for a substitution, so the speedometer, odometer and wheel-speed-derived systems stay close enough to calibration. The section width difference of +20 mm is a separate question and is the one that decides whether it rubs.

Neither figure says anything about physical fitment. Whether 205/55R16 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.