315/70R17 vs 285/75R16
New overall diameter
32.83″
was 34.36″
True speed at an indicated 60
57.3 mph
speedometer reads high
Revolutions per mile
614
was 587 · +27
Switching from 315/70R17 to 285/75R16? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 315/70R17 | 285/75R16 | Change |
|---|---|---|---|
| Overall diameter | 34.36″ | 32.83″ | −1.53″ (−4.5%) |
| Sidewall height | 8.68″ (220.5 mm) | 8.42″ (213.8 mm) | −6.8 mm |
| Tread width | 315 mm | 285 mm | −30 mm |
| Circumference | 107.95″ | 103.14″ | −4.81″ |
| Revs per mile | 587 | 614 | +27 |
| Speedometer error | baseline | −4.5% | reads high |
Diameter overlay
315/70R17 285/75R16
Speedometer check
With 285/75R16 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
23.9 mph actual
35 mph shown
33.4 mph actual
45 mph shown
43.0 mph actual
55 mph shown
52.5 mph actual
65 mph shown
62.1 mph actual
75 mph shown
71.7 mph actual
Common questions
- Will 285/75R16 fit instead of 315/70R17?
- Marginal fit — proceed with care. The 4.5% 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 higher than your true speed. Overall diameter goes from 34.36″ to 32.83″, a change of −4.5%. 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 285/75R16?
- At an indicated 60 mph you would actually be travelling about 57.3 mph — a −4.5% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 315/70R17 and 285/75R16?
- 315/70R17 turns roughly 587 revolutions per mile; 285/75R16 turns roughly 614. That is a change of +27 revolutions per mile, which is what shifts odometer and speedometer readings.