265/50R20 vs 305/50R20
New overall diameter
32.01″
was 30.43″
True speed at an indicated 60
63.1 mph
speedometer reads low
Revolutions per mile
630
was 663 · −33
Switching from 265/50R20 to 305/50R20? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 265/50R20 | 305/50R20 | Change |
|---|---|---|---|
| Overall diameter | 30.43″ | 32.01″ | +1.57″ (+5.2%) |
| Sidewall height | 5.22″ (132.5 mm) | 6.00″ (152.5 mm) | +20.0 mm |
| Tread width | 265 mm | 305 mm | +40 mm |
| Circumference | 95.61″ | 100.56″ | +4.95″ |
| Revs per mile | 663 | 630 | −33 |
| Speedometer error | baseline | +5.2% | reads low |
Diameter overlay
265/50R20 305/50R20
Speedometer check
With 305/50R20 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
68.4 mph actual
75 mph shown
78.9 mph actual
Common questions
- Will 305/50R20 fit instead of 265/50R20?
- Not recommended. A 5.2% diameter change exceeds the 5% rule. Expect significant speedometer error, potential clearance and rubbing issues, and stress on ABS, stability control and drivetrain components. Your speedometer will read lower than your true speed. Overall diameter goes from 30.43″ to 32.01″, a change of +5.2%. 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 305/50R20?
- At an indicated 60 mph you would actually be travelling about 63.1 mph — a +5.2% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 265/50R20 and 305/50R20?
- 265/50R20 turns roughly 663 revolutions per mile; 305/50R20 turns roughly 630. That is a change of −33 revolutions per mile, which is what shifts odometer and speedometer readings.