225/45R17 vs 255/65R17
New overall diameter
30.05″
was 24.97″
True speed at an indicated 60
72.2 mph
speedometer reads low
Revolutions per mile
671
was 808 · −136
Switching from 225/45R17 to 255/65R17? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 225/45R17 | 255/65R17 | Change |
|---|---|---|---|
| Overall diameter | 24.97″ | 30.05″ | +5.08″ (+20.3%) |
| Sidewall height | 3.99″ (101.3 mm) | 6.53″ (165.8 mm) | +64.5 mm |
| Tread width | 225 mm | 255 mm | +30 mm |
| Circumference | 78.45″ | 94.41″ | +15.96″ |
| Revs per mile | 808 | 671 | −136 |
| Speedometer error | baseline | +20.3% | reads low |
Diameter overlay
225/45R17 255/65R17
Speedometer check
With 255/65R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
30.1 mph actual
35 mph shown
42.1 mph actual
45 mph shown
54.2 mph actual
55 mph shown
66.2 mph actual
65 mph shown
78.2 mph actual
75 mph shown
90.3 mph actual
Common questions
- Will 255/65R17 fit instead of 225/45R17?
- Not recommended. A 20.3% 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 24.97″ to 30.05″, a change of +20.3%. 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 255/65R17?
- At an indicated 60 mph you would actually be travelling about 72.2 mph — a +20.3% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 225/45R17 and 255/65R17?
- 225/45R17 turns roughly 808 revolutions per mile; 255/65R17 turns roughly 671. That is a change of −136 revolutions per mile, which is what shifts odometer and speedometer readings.