255/50R19 vs 235/50R19
New overall diameter
28.25″
was 29.04″
True speed at an indicated 60
58.4 mph
your speedo reads high
Revolutions per mile
714
was 695, +19
| Measurement | 255/50R19 | 235/50R19 | Change |
|---|---|---|---|
| Overall diameter | 29.04″ | 28.25″ | −0.79″ (−2.7%) |
| Sidewall height | 5.02″ (127.5 mm) | 4.63″ (117.5 mm) | −10.0 mm |
| Tread width | 255 mm | 235 mm | −20 mm |
| Circumference | 91.23″ | 88.76″ | −2.47″ |
| Revs per mile | 695 | 714 | +19 |
| Speedometer error | baseline | −2.7% | reads high |
Diameter overlay
255/50R19 235/50R19
Speedometer check
With 235/50R19 fitted, when the speedometer shows the indicated speed, your actual speed is:
25 mph shown
24.3 mph actual
35 mph shown
34.1 mph actual
45 mph shown
43.8 mph actual
55 mph shown
53.5 mph actual
65 mph shown
63.2 mph actual
75 mph shown
73.0 mph actual
Common questions
- Will 235/50R19 fit instead of 255/50R19?
- Diameter moves 2.7%, 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 high, so you are going slower than it says. Overall diameter goes from 29.04″ to 28.25″, a change of −2.7%. 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 235/50R19?
- At an indicated 60 mph you are really doing about 58.4 mph, a −2.7% error. The speedometer reads high, so you are going slower than it shows.
- What is the difference in revolutions per mile between 255/50R19 and 235/50R19?
- 255/50R19 turns about 695 times per mile and 235/50R19 turns about 714, a difference of +19. Your speedometer and odometer both count rotations, so this number is what throws them off.