245/40R19 vs 235/45R19
New overall diameter
27.33″
was 26.72″
True speed at an indicated 60
61.4 mph
your speedo reads low
Revolutions per mile
738
was 755, −17
| Measurement | 245/40R19 | 235/45R19 | Change |
|---|---|---|---|
| Overall diameter | 26.72″ | 27.33″ | +0.61″ (+2.3%) |
| Sidewall height | 3.86″ (98.0 mm) | 4.16″ (105.8 mm) | +7.8 mm |
| Tread width | 245 mm | 235 mm | −10 mm |
| Circumference | 83.93″ | 85.85″ | +1.92″ |
| Revs per mile | 755 | 738 | −17 |
| Speedometer error | baseline | +2.3% | reads low |
Diameter overlay
245/40R19 235/45R19
Speedometer check
With 235/45R19 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
25.6 mph actual
35 mph shown
35.8 mph actual
45 mph shown
46.0 mph actual
55 mph shown
56.3 mph actual
65 mph shown
66.5 mph actual
75 mph shown
76.7 mph actual
Common questions
- Will 235/45R19 fit instead of 245/40R19?
- Diameter moves 2.3%, 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 26.72″ to 27.33″, a change of +2.3%. 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 235/45R19?
- At an indicated 60 mph you are really doing about 61.4 mph, a +2.3% error. The speedometer reads low, so you are going faster than it shows.
- What is the difference in revolutions per mile between 245/40R19 and 235/45R19?
- 245/40R19 turns about 755 times per mile and 235/45R19 turns about 738, a difference of −17. Your speedometer and odometer both count rotations, so this number is what throws them off.