235/75R15 vs 235/65R17
New overall diameter
29.03″
was 28.88″
True speed at an indicated 60
60.3 mph
speedometer reads low
Revolutions per mile
695
was 698 · −4
Switching from 235/75R15 to 235/65R17? Everything that changes is below — sidewall, tread width, circumference, revolutions per mile and speedometer error at road speeds.
| Measurement | 235/75R15 | 235/65R17 | Change |
|---|---|---|---|
| Overall diameter | 28.88″ | 29.03″ | +0.15″ (+0.5%) |
| Sidewall height | 6.94″ (176.3 mm) | 6.01″ (152.8 mm) | −23.5 mm |
| Tread width | 235 mm | 235 mm | +0 mm |
| Circumference | 90.72″ | 91.19″ | +0.47″ |
| Revs per mile | 698 | 695 | −4 |
| Speedometer error | baseline | +0.5% | reads low |
Diameter overlay
235/75R15 235/65R17
Speedometer check
With 235/65R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.1 mph actual
35 mph shown
35.2 mph actual
45 mph shown
45.2 mph actual
55 mph shown
55.3 mph actual
65 mph shown
65.3 mph actual
75 mph shown
75.4 mph actual
Common questions
- Will 235/65R17 fit instead of 235/75R15?
- Good fit. Within the 3% rule — overall diameter changes only 0.5%. Speedometer calibration, ABS, traction control and gearing all stay in their intended range. Your speedometer will read lower than your true speed. Overall diameter goes from 28.88″ to 29.03″, a change of +0.5%. 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 235/65R17?
- At an indicated 60 mph you would actually be travelling about 60.3 mph — a +0.5% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 235/75R15 and 235/65R17?
- 235/75R15 turns roughly 698 revolutions per mile; 235/65R17 turns roughly 695. That is a change of −4 revolutions per mile, which is what shifts odometer and speedometer readings.