235/45R18 · passenger car · Overview
Recommended pressure for 235/45R18 tyres
- Size
- 235/45R18
- Class
- passenger car
- Planning PSI
- 36
- Planning bar
- 2.48
235/45R18
36 psi / 2.48 bar
248 kPa · estimates for this size class
235/45R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
Searches for “235/45R18 pressure” usually want a number. Use 36 psi (2.48 bar) only as a sketch; the door-pillar placard on the car that wears this size still wins. A 10 °C overnight drop takes roughly 1 psi (0.07 bar) off a closed 235/45R18. 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.
What 235/45R18 means
235/45R18 means a 235 millimetre section width, a sidewall that is 45 percent of that width, on a 18-inch rim. The R is radial construction.
Common EV / sport 18-inch. Rim diameter 18 in; section 235 mm. Estimates on this page assume a typical load index for the passenger car class.
Estimated 235/45R18 pressure by load
These 235/45R18 load steps are ± a few PSI from 36. They are not a licence to ignore a printed second column on a van or estate.
| 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 |
PSI, bar and kPa
Use the table, then set a cold gauge. 248 kPa is 100 × 2.48 bar on this size.
| PSI | Bar | kPa |
|---|---|---|
| 32 | 2.21 | 221 |
| 33 | 2.28 | 228 |
| 34 | 2.34 | 234 |
| 35 | 2.41 | 241 |
| 36 | 2.48 | 248 |
| 37 | 2.55 | 255 |
| 38 | 2.62 | 262 |
| 39 | 2.69 | 269 |
| 40 | 2.76 | 276 |
| 41 | 2.83 | 283 |
| 42 | 2.90 | 290 |
| 43 | 2.96 | 296 |
| 44 | 3.03 | 303 |
| 45 | 3.10 | 310 |
| 46 | 3.17 | 317 |
| 47 | 3.24 | 324 |
| 48 | 3.31 | 331 |
Placard versus sidewall
The sidewall of a 235/45R18 may say 51 psi or 350 kPa. That is a carcass maximum. Operating pressure is the tyre-information placard on the driver’s door pillar.
Cars often seen on 235/45R18
These catalogue models are often seen on 235/45R18 or a close OEM neighbour. Open the vehicle chart for axle-specific PSI and bar.
How to set 235/45R18
- Measure before the school run, not after the motorway.
- Write LF / RF / RR / RL. Do not keep 235/45R18 numbers in your head.
- Add air in short bursts toward the placard, using 36 psi only as a map.
- If one 235/45R18 is 4 psi down, hunt for a nail before you blame the weather.
- Log date, ambient temperature and the four readings.
Temperature drift
Roughly 1 psi per 5–6 °C. The table uses 36 psi as a 20 °C baseline for 235/45R18.
| 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 235/45R18 |
| 38 °C (heatwave tarmac) | 39 psi | 2.69 bar | 269 kPa | Do not bleed a hot 235/45R18 |
Keep 235/45R18 on the printed band for that car; 36 psi is a size sketch, not a second VIN label.
Questions about 235/45R18
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.
Is the sidewall number correct for 235/45R18?
No. Sidewall PSI or kPa is a maximum for the carcass. Operating pressure is the door-pillar placard.
Can I run 235/45R18 at a lower pressure for comfort?
Not as a habit. A soft 235/45R18 cooks the shoulders and dulls steering. Keep load index and stay on the placard.
Is 235/45R18 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.
What PSI should 235/45R18 tyres be?
A passenger car planning figure is about 36 psi cold (2.48 bar / 248 kPa). Confirm on the vehicle placard — two cars can share 235/45R18 and not share a sticker.
Handbook: placard · bar vs PSI · cold inflation · all sizes