235/80R17 vs 245/70R17
New overall diameter
30.50″
was 31.80″
True speed at an indicated 60
57.5 mph
your speedo reads high
Revolutions per mile
661
was 634, +27
| Measurement | 235/80R17 | 245/70R17 | Change |
|---|---|---|---|
| Overall diameter | 31.80″ | 30.50″ | −1.30″ (−4.1%) |
| Sidewall height | 7.40″ (188.0 mm) | 6.75″ (171.5 mm) | −16.5 mm |
| Tread width | 235 mm | 245 mm | +10 mm |
| Circumference | 99.91″ | 95.83″ | −4.08″ |
| Revs per mile | 634 | 661 | +27 |
| Speedometer error | baseline | −4.1% | reads high |
Diameter overlay
235/80R17 245/70R17
Speedometer check
With 245/70R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
24.0 mph actual
35 mph shown
33.6 mph actual
45 mph shown
43.2 mph actual
55 mph shown
52.8 mph actual
65 mph shown
62.3 mph actual
75 mph shown
71.9 mph actual
Common questions
- Will 245/70R17 fit instead of 235/80R17?
- Overall diameter changes 4.1%; section width changes 10 mm. Diameter comparison alone cannot confirm fitment. Verify the vehicle maker's approved rim width, tire load and speed ratings, and clearance at full steering lock and suspension compression. Confirm any possible ABS, traction-control, speedometer, and drivetrain effects with the vehicle maker or a qualified tire professional. Overall diameter goes from 31.80″ to 30.50″, a change of −4.1%. The rule of thumb most shops use: under 3% is fine, 3 to 5% needs a clearance check, over 5% needs recalibration.
- How far off will my speedometer read on 245/70R17?
- At an indicated 60 mph you are really doing about 57.5 mph, a −4.1% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 235/80R17 and 245/70R17?
- 235/80R17 turns about 634 times per mile and 245/70R17 turns about 661, a difference of +27. Your speedometer and odometer both count rotations, so this number is what throws them off.