305/65R17 vs 265/70R18
New overall diameter
32.61″
was 32.61″
True speed at an indicated 60
60.0 mph
no meaningful change
Revolutions per mile
619
was 618 · +0
Switching from 305/65R17 to 265/70R18? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 305/65R17 | 265/70R18 | Change |
|---|---|---|---|
| Overall diameter | 32.61″ | 32.61″ | −0.00″ (−0.0%) |
| Sidewall height | 7.81″ (198.3 mm) | 7.30″ (185.5 mm) | −12.8 mm |
| Tread width | 305 mm | 265 mm | −40 mm |
| Circumference | 102.45″ | 102.44″ | −0.01″ |
| Revs per mile | 618 | 619 | +0 |
| Speedometer error | baseline | −0.0% | no change |
Diameter overlay
305/65R17 265/70R18
Speedometer check
With 265/70R18 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.0 mph actual
35 mph shown
35.0 mph actual
45 mph shown
45.0 mph actual
55 mph shown
55.0 mph actual
65 mph shown
65.0 mph actual
75 mph shown
75.0 mph actual
Common questions
- Will 265/70R18 fit instead of 305/65R17?
- Good fit. Within the 3% rule — overall diameter changes only 0.0%. Speedometer calibration, ABS, traction control and gearing all stay in their intended range. Speedometer accuracy is essentially unchanged. Overall diameter goes from 32.61″ to 32.61″, a change of −0.0%. 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 265/70R18?
- At an indicated 60 mph you would actually be travelling about 60.0 mph — a −0.0% error. That is effectively no change.
- What is the difference in revolutions per mile between 305/65R17 and 265/70R18?
- 305/65R17 turns roughly 618 revolutions per mile; 265/70R18 turns roughly 619. That is a change of +0 revolutions per mile, which is what shifts odometer and speedometer readings.