185/60R15 vs 225/45R17
New overall diameter
24.97″
was 23.74″
True speed at an indicated 60
63.1 mph
your speedo reads low
Revolutions per mile
808
was 850, −42
| Measurement | 185/60R15 | 225/45R17 | Change |
|---|---|---|---|
| Overall diameter | 23.74″ | 24.97″ | +1.23″ (+5.2%) |
| Sidewall height | 4.37″ (111.0 mm) | 3.99″ (101.3 mm) | −9.8 mm |
| Tread width | 185 mm | 225 mm | +40 mm |
| Circumference | 74.58″ | 78.45″ | +3.87″ |
| Revs per mile | 850 | 808 | −42 |
| Speedometer error | baseline | +5.2% | reads low |
Diameter overlay
185/60R15 225/45R17
Speedometer check
With 225/45R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
26.3 mph actual
35 mph shown
36.8 mph actual
45 mph shown
47.3 mph actual
55 mph shown
57.9 mph actual
65 mph shown
68.4 mph actual
75 mph shown
78.9 mph actual
Common questions
- Will 225/45R17 fit instead of 185/60R15?
- 5.2% is past the 5% mark, which is where this stops being a tire choice and starts being a project. Expect rubbing, meaningful speedometer error, and extra load on ABS, stability control and the drivetrain. Recalibration is the usual fix. Your speedometer will read low, so you are going faster than it says. Overall diameter goes from 23.74″ to 24.97″, a change of +5.2%. 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 225/45R17?
- At an indicated 60 mph you are really doing about 63.1 mph, a +5.2% 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 225/45R17?
- 185/60R15 turns about 850 times per mile and 225/45R17 turns about 808, a difference of −42. Your speedometer and odometer both count rotations, so this number is what throws them off.