235/45R18 · passenger car · PSI
235/45R18 tyre pressure in PSI
- Size
- 235/45R18
- Class
- passenger car
- Planning PSI
- 36
- Planning bar
- 2.48
psi
36
2.48 bar · 248 kPa · passenger car planning figure
235/45R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
PSI is the garage-hose number. For 235/45R18 a typical passenger car planning figure is 36 psi cold — about 2.48 bar or 248 kPa. TPMS typically warns near 27 psi (about 25% below a 36 psi target). That is already a soft tyre. 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.
Estimated 235/45R18 pressure by load
Plus-sizing to 235/45R18 from a taller OEM tyre usually keeps the same placard if the load index is equal or higher.
| Condition | Front (est.) | Rear (est.) |
|---|---|---|
| Driver only / unladen | 36 psi / 2.48 bar / 248 kPa | 36 psi / 2.48 bar / 248 kPa |
| Typical occupancy | 37 psi / 2.55 bar / 255 kPa | 38 psi / 2.62 bar / 262 kPa |
| Motorway + luggage (sketch) | 38 psi / 2.62 bar / 262 kPa | 39 psi / 2.69 bar / 269 kPa |
PSI, bar and kPa
Convert around the 235/45R18 band. 2.48 bar is about 36 psi — not 23, not 33 unless the maths says so.
| 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 |
What 235/45R18 means
Read 235/45R18 as width / aspect R rim. Nothing in the size string is a pressure. Pressure lives on the car, not moulded as 205 or 55.
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.
Placard versus sidewall
This website maps size searches such as “235/45R18 psi”. It does not replace the VIN label. If the two disagree, the label wins.
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
- Park so the 235/45R18 tyres are cold (three hours, or less than about a mile).
- Read the door-pillar placard for that car — not the 235/45R18 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.
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 |
A cheap gauge and a monthly habit will do more for a set of 235/45R18 than nitrogen upsells.
Questions about 235/45R18
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.
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.
What is 235/45R18 in bar?
36 psi is 2.48 bar. Add a tenth of a bar if the placard’s laden column is higher, which is common on vans that wear this size.
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.
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.
Handbook: placard · bar vs PSI · cold inflation · all sizes