245/45R17 vs 225/55R17
New overall diameter
26.74″
was 25.68″
True speed at an indicated 60
62.5 mph
speedometer reads low
Revolutions per mile
754
was 785 · −31
Switching from 245/45R17 to 225/55R17? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 245/45R17 | 225/55R17 | Change |
|---|---|---|---|
| Overall diameter | 25.68″ | 26.74″ | +1.06″ (+4.1%) |
| Sidewall height | 4.34″ (110.3 mm) | 4.87″ (123.8 mm) | +13.5 mm |
| Tread width | 245 mm | 225 mm | −20 mm |
| Circumference | 80.68″ | 84.02″ | +3.34″ |
| Revs per mile | 785 | 754 | −31 |
| Speedometer error | baseline | +4.1% | reads low |
Diameter overlay
245/45R17 225/55R17
Speedometer check
With 225/55R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
26.0 mph actual
35 mph shown
36.4 mph actual
45 mph shown
46.9 mph actual
55 mph shown
57.3 mph actual
65 mph shown
67.7 mph actual
75 mph shown
78.1 mph actual
Common questions
- Will 225/55R17 fit instead of 245/45R17?
- Marginal fit — proceed with care. The 4.1% 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 lower than your true speed. Overall diameter goes from 25.68″ to 26.74″, a change of +4.1%. 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 225/55R17?
- At an indicated 60 mph you would actually be travelling about 62.5 mph — a +4.1% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 245/45R17 and 225/55R17?
- 245/45R17 turns roughly 785 revolutions per mile; 225/55R17 turns roughly 754. That is a change of −31 revolutions per mile, which is what shifts odometer and speedometer readings.