225/45R18 · passenger car · kPa
225/45R18 tyre pressure in kPa
- Size
- 225/45R18
- Class
- passenger car
- Planning PSI
- 36
- Planning bar
- 2.48
kPa
248
2.48 bar · 36 psi · 100 kPa = 1 bar
225/45R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
If the gauge only speaks kPa, 248 kPa is the sketch for this passenger car size. Fine-tune to the vehicle that actually wears 225/45R18. Under-inflation cooks the shoulders of a 225/45R18; over-inflation wears the centre rib and bangs every cat’s eye. Low-profile {sz} does not want a “softer” pressure to recover ride. Stay at or slightly above the car’s original placard if load index is kept.
kPa, bar and PSI
Use the table, then set a cold gauge. 248 kPa is 100 × 2.48 bar on this size.
| kPa | Bar | PSI |
|---|---|---|
| 221 | 2.21 | 32 |
| 228 | 2.28 | 33 |
| 234 | 2.34 | 34 |
| 241 | 2.41 | 35 |
| 248 | 2.48 | 36 |
| 255 | 2.55 | 37 |
| 262 | 2.62 | 38 |
| 269 | 2.69 | 39 |
| 276 | 2.76 | 40 |
| 283 | 2.83 | 41 |
| 290 | 2.90 | 42 |
| 296 | 2.96 | 43 |
| 303 | 3.03 | 44 |
| 310 | 3.10 | 45 |
| 317 | 3.17 | 46 |
| 324 | 3.24 | 47 |
| 331 | 3.31 | 48 |
Estimated 225/45R18 pressure by load
Load moves the rear first on a passenger car. If the factory placard already has a laden column, use that — not this sketch for 225/45R18.
| Condition | Front (est.) | Rear (est.) |
|---|---|---|
| Driver only / unladen | 36 psi / 2.48 bar / 248 kPa | 36 psi / 2.48 bar / 248 kPa |
| Typical occupancy | 36 psi / 2.48 bar / 248 kPa | 37 psi / 2.55 bar / 255 kPa |
| Motorway + luggage (sketch) | 37 psi / 2.55 bar / 255 kPa | 38 psi / 2.62 bar / 262 kPa |
What 225/45R18 means
225/45R18 means a 225 millimetre section width, a sidewall that is 45 percent of that width, on a 18-inch rim. The R is radial construction.
18-inch sport compact / EV. Rim diameter 18 in; section 225 mm. Estimates on this page assume a typical load index for the passenger car class.
Placard versus sidewall
If a forum says “all 225/45R18 run 36 psi”, ignore it. A Qashqai and a Golf can share a size and not share a sticker.
Temperature drift
Roughly 1 psi per 5–6 °C. The table uses 36 psi as a 20 °C baseline for 225/45R18.
| Ambient | Gauge | Bar | kPa | Note |
|---|---|---|---|---|
| −5 °C (hard frost) | 33 psi | 2.28 bar | 228 kPa | Gauge reads low; do not overfill once warm |
| 0 °C | 34 psi | 2.34 bar | 234 kPa | Gauge reads low; do not overfill once warm |
| 8 °C (UK winter morning) | 35 psi | 2.41 bar | 241 kPa | Gauge reads low; do not overfill once warm |
| 20 °C (set cold here) | 36 psi | 2.48 bar | 248 kPa | Baseline for this size sketch |
| 30 °C | 38 psi | 2.62 bar | 262 kPa | Do not bleed a hot 225/45R18 |
| 38 °C (heatwave tarmac) | 39 psi | 2.69 bar | 269 kPa | Do not bleed a hot 225/45R18 |
How to set 225/45R18
- Park so the 225/45R18 tyres are cold (three hours, or less than about a mile).
- Read the door-pillar placard for that car — not the 225/45R18 sidewall maximum.
- If the sticker is missing, 36 psi / 2.48 bar is only a passenger car planning figure for this size.
- Set all four with a calibrated gauge. A 3 psi miss on one corner shows up as a wander.
- Refit valve caps and reset TPMS if the handbook asks for a relearn.
Cars often seen on 225/45R18
These catalogue models are often seen on 225/45R18 or a close OEM neighbour. Open the vehicle chart for axle-specific PSI and bar.
Keep 225/45R18 on the printed band for that car; 36 psi is a size sketch, not a second VIN label.
Questions about 225/45R18
Is the sidewall number correct for 225/45R18?
No. Sidewall PSI or kPa is a maximum for the carcass. Operating pressure is the door-pillar placard.
Is 225/45R18 the same as a plus-size swap?
Only if that is the size you fitted. Overall diameter should stay close to OEM. Pressure still follows the car, with load index at or above original.
When does TPMS warn on 225/45R18?
Direct TPMS typically flags about 25% below target — near 27 psi if you were aiming at 36. Fill to the sticker, not to the lamp.
Should I bleed pressure after a motorway run?
No. Heat raises the gauge. Set cold only. Bleeding a hot tyre leaves it low the next morning.
What is 225/45R18 in kPa?
248 kPa is the planning midpoint (100 kPa = 1 bar). 255 kPa is one PSI higher.
Handbook: placard · bar vs PSI · cold inflation · all sizes