185/60R15 vs 205/55R16
New overall diameter
24.88″
was 23.74″
True speed at an indicated 60
62.9 mph
speedometer reads low
Revolutions per mile
811
was 850 · −39
Switching from 185/60R15 to 205/55R16? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 185/60R15 | 205/55R16 | Change |
|---|---|---|---|
| Overall diameter | 23.74″ | 24.88″ | +1.14″ (+4.8%) |
| Sidewall height | 4.37″ (111.0 mm) | 4.44″ (112.8 mm) | +1.8 mm |
| Tread width | 185 mm | 205 mm | +20 mm |
| Circumference | 74.58″ | 78.16″ | +3.57″ |
| Revs per mile | 850 | 811 | −39 |
| Speedometer error | baseline | +4.8% | reads low |
Diameter overlay
185/60R15 205/55R16
Speedometer check
With 205/55R16 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
26.2 mph actual
35 mph shown
36.7 mph actual
45 mph shown
47.2 mph actual
55 mph shown
57.6 mph actual
65 mph shown
68.1 mph actual
75 mph shown
78.6 mph actual
Common questions
- Will 205/55R16 fit instead of 185/60R15?
- Marginal fit — proceed with care. The 4.8% diameter change is between 3% and 5%. It can work, but expect noticeable speedometer error and check wheel-well clearance, scrub radius and gearing before committing. Your speedometer will read lower than your true speed. Overall diameter goes from 23.74″ to 24.88″, a change of +4.8%. As a rule of thumb, under 3% is safe, 3–5% needs a clearance check, and over 5% is not recommended.
- How far off will my speedometer read on 205/55R16?
- At an indicated 60 mph you would actually be travelling about 62.9 mph — a +4.8% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 185/60R15 and 205/55R16?
- 185/60R15 turns roughly 850 revolutions per mile; 205/55R16 turns roughly 811. That is a change of −39 revolutions per mile, which is what shifts odometer and speedometer readings.