235/45R18 vs 265/70R18
New overall diameter
32.61″
was 26.33″
True speed at an indicated 60
74.3 mph
your speedo reads low
Revolutions per mile
619
was 766, −148
| Measurement | 235/45R18 | 265/70R18 | Change |
|---|---|---|---|
| Overall diameter | 26.33″ | 32.61″ | +6.28″ (+23.9%) |
| Sidewall height | 4.16″ (105.8 mm) | 7.30″ (185.5 mm) | +79.8 mm |
| Tread width | 235 mm | 265 mm | +30 mm |
| Circumference | 82.71″ | 102.44″ | +19.73″ |
| Revs per mile | 766 | 619 | −148 |
| Speedometer error | baseline | +23.9% | reads low |
Diameter overlay
235/45R18 265/70R18
Speedometer check
With 265/70R18 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
31.0 mph actual
35 mph shown
43.3 mph actual
45 mph shown
55.7 mph actual
55 mph shown
68.1 mph actual
65 mph shown
80.5 mph actual
75 mph shown
92.9 mph actual
Common questions
- Will 265/70R18 fit instead of 235/45R18?
- Overall diameter changes 23.9%; section width changes 30 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 26.33″ to 32.61″, a change of +23.9%. 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 265/70R18?
- At an indicated 60 mph you are really doing about 74.3 mph, a +23.9% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 235/45R18 and 265/70R18?
- 235/45R18 turns about 766 times per mile and 265/70R18 turns about 619, a difference of −148. Your speedometer and odometer both count rotations, so this number is what throws them off.