185/65R15 vs 185/60R15
New overall diameter
23.74″
was 24.47″
True speed at an indicated 60
58.2 mph
your speedo reads high
Revolutions per mile
850
was 824, +25
| Measurement | 185/65R15 | 185/60R15 | Change |
|---|---|---|---|
| Overall diameter | 24.47″ | 23.74″ | −0.73″ (−3.0%) |
| Sidewall height | 4.73″ (120.3 mm) | 4.37″ (111.0 mm) | −9.3 mm |
| Tread width | 185 mm | 185 mm | +0 mm |
| Circumference | 76.87″ | 74.58″ | −2.29″ |
| Revs per mile | 824 | 850 | +25 |
| Speedometer error | baseline | −3.0% | reads high |
Diameter overlay
185/65R15 185/60R15
Speedometer check
With 185/60R15 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
24.3 mph actual
35 mph shown
34.0 mph actual
45 mph shown
43.7 mph actual
55 mph shown
53.4 mph actual
65 mph shown
63.1 mph actual
75 mph shown
72.8 mph actual
Common questions
- Will 185/60R15 fit instead of 185/65R15?
- Diameter moves 3.0%, comfortably inside the 3% rule. Your speedometer, ABS, traction control and gearing all stay in the range they were calibrated for. Your speedometer will read high, so you are going slower than it says. Overall diameter goes from 24.47″ to 23.74″, a change of −3.0%. The rule of thumb most shops use: under 3% is fine, 3 to 5% needs a clearance check, over 5% needs recalibration.
- How far off will my speedometer read on 185/60R15?
- At an indicated 60 mph you are really doing about 58.2 mph, a −3.0% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 185/65R15 and 185/60R15?
- 185/65R15 turns about 824 times per mile and 185/60R15 turns about 850, a difference of +25. Your speedometer and odometer both count rotations, so this number is what throws them off.