255/70R17 vs 255/75R17
New overall diameter
32.06″
was 31.06″
True speed at an indicated 60
61.9 mph
your speedo reads low
Revolutions per mile
629
was 649, −20
| Measurement | 255/70R17 | 255/75R17 | Change |
|---|---|---|---|
| Overall diameter | 31.06″ | 32.06″ | +1.00″ (+3.2%) |
| Sidewall height | 7.03″ (178.5 mm) | 7.53″ (191.3 mm) | +12.8 mm |
| Tread width | 255 mm | 255 mm | +0 mm |
| Circumference | 97.56″ | 100.72″ | +3.15″ |
| Revs per mile | 649 | 629 | −20 |
| Speedometer error | baseline | +3.2% | reads low |
Diameter overlay
255/70R17 255/75R17
Speedometer check
With 255/75R17 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.8 mph actual
35 mph shown
36.1 mph actual
45 mph shown
46.5 mph actual
55 mph shown
56.8 mph actual
65 mph shown
67.1 mph actual
75 mph shown
77.4 mph actual
Common questions
- Will 255/75R17 fit instead of 255/70R17?
- Overall diameter changes 3.2%; section width changes 0 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 31.06″ to 32.06″, a change of +3.2%. 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 255/75R17?
- At an indicated 60 mph you are really doing about 61.9 mph, a +3.2% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 255/70R17 and 255/75R17?
- 255/70R17 turns about 649 times per mile and 255/75R17 turns about 629, a difference of −20. Your speedometer and odometer both count rotations, so this number is what throws them off.