185/65R15 vs 215/50R17
New overall diameter
25.46″
was 24.47″
True speed at an indicated 60
62.4 mph
your speedo reads low
Revolutions per mile
792
was 824, −32
| Measurement | 185/65R15 | 215/50R17 | Change |
|---|---|---|---|
| Overall diameter | 24.47″ | 25.46″ | +1.00″ (+4.1%) |
| Sidewall height | 4.73″ (120.3 mm) | 4.23″ (107.5 mm) | −12.8 mm |
| Tread width | 185 mm | 215 mm | +30 mm |
| Circumference | 76.87″ | 80.00″ | +3.13″ |
| Revs per mile | 824 | 792 | −32 |
| Speedometer error | baseline | +4.1% | reads low |
Diameter overlay
185/65R15 215/50R17
Speedometer check
With 215/50R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
26.0 mph actual
35 mph shown
36.4 mph actual
45 mph shown
46.8 mph actual
55 mph shown
57.2 mph actual
65 mph shown
67.6 mph actual
75 mph shown
78.1 mph actual
Common questions
- Will 215/50R17 fit instead of 185/65R15?
- At 4.1% this lands between the 3% and 5% marks. Plenty of people run swaps like this, but you will see real speedometer error, and you want to check the wheel well at full lock and full compression before you buy. Your speedometer will read low, so you are going faster than it says. Overall diameter goes from 24.47″ to 25.46″, a change of +4.1%. 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 215/50R17?
- At an indicated 60 mph you are really doing about 62.4 mph, a +4.1% 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 215/50R17?
- 185/65R15 turns about 824 times per mile and 215/50R17 turns about 792, a difference of −32. Your speedometer and odometer both count rotations, so this number is what throws them off.