225/45R17 vs 245/75R17
New overall diameter
31.47″
was 24.97″
True speed at an indicated 60
75.6 mph
speedometer reads low
Revolutions per mile
641
was 808 · −167
Switching from 225/45R17 to 245/75R17? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 225/45R17 | 245/75R17 | Change |
|---|---|---|---|
| Overall diameter | 24.97″ | 31.47″ | +6.50″ (+26.0%) |
| Sidewall height | 3.99″ (101.3 mm) | 7.23″ (183.8 mm) | +82.5 mm |
| Tread width | 225 mm | 245 mm | +20 mm |
| Circumference | 78.45″ | 98.86″ | +20.41″ |
| Revs per mile | 808 | 641 | −167 |
| Speedometer error | baseline | +26.0% | reads low |
Diameter overlay
225/45R17 245/75R17
Speedometer check
With 245/75R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
31.5 mph actual
35 mph shown
44.1 mph actual
45 mph shown
56.7 mph actual
55 mph shown
69.3 mph actual
65 mph shown
81.9 mph actual
75 mph shown
94.5 mph actual
Common questions
- Will 245/75R17 fit instead of 225/45R17?
- Not recommended. A 26.0% 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 31.47″, a change of +26.0%. 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 245/75R17?
- At an indicated 60 mph you would actually be travelling about 75.6 mph — a +26.0% 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 245/75R17?
- 225/45R17 turns roughly 808 revolutions per mile; 245/75R17 turns roughly 641. That is a change of −167 revolutions per mile, which is what shifts odometer and speedometer readings.