Tire size comparison
225/45R18 vs 235/40R19
Overall diameter, sidewall, revs per mile, and speedometer error — 235/40R19 is the taller tire, with a 1.7% speedo delta when swapping.
225/45R18
25.97in
660 mm overall diameter
235/40R19
26.4in
671 mm overall diameter
Diameter Δ
0.43 in
Speedo error
1.7%
225/45R18 revs/mi
777
235/40R19 revs/mi
764
Within the ±3% overall-diameter band usually considered safe for plus-sizing — speedometer and ABS calibration should stay close to factory.
Full spec
Side by side
| Metric | 225/45R18 | 235/40R19 |
|---|---|---|
| Section width | 225 mm | 235 mm |
| Aspect ratio | 45 | 40 |
| Wheel diameter | 18″ | 19″ |
| Sidewall height | 101 mm | 94 mm |
| Overall diameter | 25.97 in (660 mm) | 26.4 in (671 mm) |
| Circumference | 81.59 in | 82.94 in |
| Revolutions / mile | 777 | 764 |
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FAQ
Frequently asked
- What is the diameter difference between 225/45R18 and 235/40R19?
- 225/45R18 has an overall diameter of 25.97 inches (660 mm). 235/40R19 is 26.4 inches (671 mm). That's a 0.43 inch (11 mm) difference — 235/40R19 is taller.
- Will 235/40R19 cause speedometer error on a car fitted with 225/45R18?
- Swapping 225/45R18 for 235/40R19 produces a speedometer error of about 1.7%. Your speedometer will read lower than your actual speed — a 60 mph indicated reading is really 61 mph. Anything under 3% is usually acceptable without recalibration.
- How many revolutions per mile does each size do?
- 225/45R18 turns 777 revs per mile. 235/40R19 turns 764 revs per mile. Taller tyres turn fewer times per mile, which lowers effective final-drive ratio.
- What's the sidewall height difference?
- 225/45R18 has a sidewall of 101 mm (3.99 in). 235/40R19 sidewall is 94 mm (3.7 in). Lower-profile sidewalls give sharper steering response but less bump compliance.
- Is 235/40R19 a safe plus-size upgrade from 225/45R18?
- A plus-size upgrade is considered safe when overall diameter stays within ±3% — here the difference is 1.7%. This swap is within the typical safe range; speedometer and ABS calibration should remain close to factory.
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