275/70R17 vs 245/70R17
New overall diameter
30.50″
was 32.16″
True speed at an indicated 60
56.9 mph
speedometer reads high
Revolutions per mile
661
was 627 · +34
Switching from 275/70R17 to 245/70R17? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 275/70R17 | 245/70R17 | Change |
|---|---|---|---|
| Overall diameter | 32.16″ | 30.50″ | −1.65″ (−5.1%) |
| Sidewall height | 7.58″ (192.5 mm) | 6.75″ (171.5 mm) | −21.0 mm |
| Tread width | 275 mm | 245 mm | −30 mm |
| Circumference | 101.03″ | 95.83″ | −5.19″ |
| Revs per mile | 627 | 661 | +34 |
| Speedometer error | baseline | −5.1% | reads high |
Diameter overlay
275/70R17 245/70R17
Speedometer check
With 245/70R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
23.7 mph actual
35 mph shown
33.2 mph actual
45 mph shown
42.7 mph actual
55 mph shown
52.2 mph actual
65 mph shown
61.7 mph actual
75 mph shown
71.1 mph actual
Common questions
- Will 245/70R17 fit instead of 275/70R17?
- Not recommended. A 5.1% 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 higher than your true speed. Overall diameter goes from 32.16″ to 30.50″, a change of −5.1%. 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 245/70R17?
- At an indicated 60 mph you would actually be travelling about 56.9 mph — a −5.1% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 275/70R17 and 245/70R17?
- 275/70R17 turns roughly 627 revolutions per mile; 245/70R17 turns roughly 661. That is a change of +34 revolutions per mile, which is what shifts odometer and speedometer readings.