185/65R15 vs 215/45R17
New overall diameter
24.62″
was 24.47″
True speed at an indicated 60
60.4 mph
your speedo reads low
Revolutions per mile
819
was 824, −5
| Measurement | 185/65R15 | 215/45R17 | Change |
|---|---|---|---|
| Overall diameter | 24.47″ | 24.62″ | +0.15″ (+0.6%) |
| Sidewall height | 4.73″ (120.3 mm) | 3.81″ (96.8 mm) | −23.5 mm |
| Tread width | 185 mm | 215 mm | +30 mm |
| Circumference | 76.87″ | 77.34″ | +0.47″ |
| Revs per mile | 824 | 819 | −5 |
| Speedometer error | baseline | +0.6% | reads low |
Diameter overlay
185/65R15 215/45R17
Speedometer check
With 215/45R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.2 mph actual
35 mph shown
35.2 mph actual
45 mph shown
45.3 mph actual
55 mph shown
55.3 mph actual
65 mph shown
65.4 mph actual
75 mph shown
75.5 mph actual
Common questions
- Will 215/45R17 fit instead of 185/65R15?
- Diameter moves 0.6%, 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 low, so you are going faster than it says. Overall diameter goes from 24.47″ to 24.62″, a change of +0.6%. 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 215/45R17?
- At an indicated 60 mph you are really doing about 60.4 mph, a +0.6% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 185/65R15 and 215/45R17?
- 185/65R15 turns about 824 times per mile and 215/45R17 turns about 819, a difference of −5. Your speedometer and odometer both count rotations, so this number is what throws them off.