275/40R20 vs 265/35R20
New overall diameter
27.30″
was 28.66″
True speed at an indicated 60
57.2 mph
speedometer reads high
Revolutions per mile
739
was 704 · +35
Switching from 275/40R20 to 265/35R20? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 275/40R20 | 265/35R20 | Change |
|---|---|---|---|
| Overall diameter | 28.66″ | 27.30″ | −1.36″ (−4.7%) |
| Sidewall height | 4.33″ (110.0 mm) | 3.65″ (92.8 mm) | −17.3 mm |
| Tread width | 275 mm | 265 mm | −10 mm |
| Circumference | 90.04″ | 85.78″ | −4.27″ |
| Revs per mile | 704 | 739 | +35 |
| Speedometer error | baseline | −4.7% | reads high |
Diameter overlay
275/40R20 265/35R20
Speedometer check
With 265/35R20 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
42.9 mph actual
55 mph shown
52.4 mph actual
65 mph shown
61.9 mph actual
75 mph shown
71.4 mph actual
Common questions
- Will 265/35R20 fit instead of 275/40R20?
- Marginal fit — proceed with care. The 4.7% 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 28.66″ to 27.30″, a change of −4.7%. 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 265/35R20?
- At an indicated 60 mph you would actually be travelling about 57.2 mph — a −4.7% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 275/40R20 and 265/35R20?
- 275/40R20 turns roughly 704 revolutions per mile; 265/35R20 turns roughly 739. That is a change of +35 revolutions per mile, which is what shifts odometer and speedometer readings.