295/70R18 vs 285/65R18
New overall diameter
32.59″
was 34.26″
True speed at an indicated 60
57.1 mph
speedometer reads high
Revolutions per mile
619
was 589 · +30
Switching from 295/70R18 to 285/65R18? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 295/70R18 | 285/65R18 | Change |
|---|---|---|---|
| Overall diameter | 34.26″ | 32.59″ | −1.67″ (−4.9%) |
| Sidewall height | 8.13″ (206.5 mm) | 7.29″ (185.3 mm) | −21.3 mm |
| Tread width | 295 mm | 285 mm | −10 mm |
| Circumference | 107.63″ | 102.37″ | −5.26″ |
| Revs per mile | 589 | 619 | +30 |
| Speedometer error | baseline | −4.9% | reads high |
Diameter overlay
295/70R18 285/65R18
Speedometer check
With 285/65R18 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
23.8 mph actual
35 mph shown
33.3 mph actual
45 mph shown
42.8 mph actual
55 mph shown
52.3 mph actual
65 mph shown
61.8 mph actual
75 mph shown
71.3 mph actual
Common questions
- Will 285/65R18 fit instead of 295/70R18?
- Marginal fit — proceed with care. The 4.9% 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 34.26″ to 32.59″, a change of −4.9%. 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 285/65R18?
- At an indicated 60 mph you would actually be travelling about 57.1 mph — a −4.9% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 295/70R18 and 285/65R18?
- 295/70R18 turns roughly 589 revolutions per mile; 285/65R18 turns roughly 619. That is a change of +30 revolutions per mile, which is what shifts odometer and speedometer readings.