235/75R15 vs 265/70R15
New overall diameter
29.61″
was 28.88″
True speed at an indicated 60
61.5 mph
your speedo reads low
Revolutions per mile
681
was 698, −17
| Measurement | 235/75R15 | 265/70R15 | Change |
|---|---|---|---|
| Overall diameter | 28.88″ | 29.61″ | +0.73″ (+2.5%) |
| Sidewall height | 6.94″ (176.3 mm) | 7.30″ (185.5 mm) | +9.3 mm |
| Tread width | 235 mm | 265 mm | +30 mm |
| Circumference | 90.72″ | 93.01″ | +2.29″ |
| Revs per mile | 698 | 681 | −17 |
| Speedometer error | baseline | +2.5% | reads low |
Diameter overlay
235/75R15 265/70R15
Speedometer check
With 265/70R15 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.6 mph actual
35 mph shown
35.9 mph actual
45 mph shown
46.1 mph actual
55 mph shown
56.4 mph actual
65 mph shown
66.6 mph actual
75 mph shown
76.9 mph actual
Common questions
- Will 265/70R15 fit instead of 235/75R15?
- Diameter moves 2.5%, comfortably inside the 3% rule. Your speedometer, ABS, traction control and gearing all stay in the range they were calibrated for. Your speedometer will read low, so you are going faster than it says. Overall diameter goes from 28.88″ to 29.61″, a change of +2.5%. 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 265/70R15?
- At an indicated 60 mph you are really doing about 61.5 mph, a +2.5% 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 265/70R15?
- 235/75R15 turns about 698 times per mile and 265/70R15 turns about 681, a difference of −17. Your speedometer and odometer both count rotations, so this number is what throws them off.