265/35R20 vs 245/45R20
New overall diameter
28.68″
was 27.30″
True speed at an indicated 60
63.0 mph
your speedo reads low
Revolutions per mile
703
was 739, −35
| Measurement | 265/35R20 | 245/45R20 | Change |
|---|---|---|---|
| Overall diameter | 27.30″ | 28.68″ | +1.38″ (+5.0%) |
| Sidewall height | 3.65″ (92.8 mm) | 4.34″ (110.3 mm) | +17.5 mm |
| Tread width | 265 mm | 245 mm | −20 mm |
| Circumference | 85.78″ | 90.10″ | +4.33″ |
| Revs per mile | 739 | 703 | −35 |
| Speedometer error | baseline | +5.0% | reads low |
Diameter overlay
265/35R20 245/45R20
Speedometer check
With 245/45R20 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
26.3 mph actual
35 mph shown
36.8 mph actual
45 mph shown
47.3 mph actual
55 mph shown
57.8 mph actual
65 mph shown
68.3 mph actual
75 mph shown
78.8 mph actual
Common questions
- Will 245/45R20 fit instead of 265/35R20?
- Overall diameter changes 5.0%; section width changes -20 mm. Diameter comparison alone cannot confirm fitment. Verify the vehicle maker's approved rim width, tire load and speed ratings, and clearance at full steering lock and suspension compression. Confirm any possible ABS, traction-control, speedometer, and drivetrain effects with the vehicle maker or a qualified tire professional. Overall diameter goes from 27.30″ to 28.68″, a change of +5.0%. 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 245/45R20?
- At an indicated 60 mph you are really doing about 63.0 mph, a +5.0% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 265/35R20 and 245/45R20?
- 265/35R20 turns about 739 times per mile and 245/45R20 turns about 703, a difference of −35. Your speedometer and odometer both count rotations, so this number is what throws them off.