245/40R18 · passenger car · Overview
Recommended pressure for 245/40R18 tyres
- Size
- 245/40R18
- Class
- passenger car
- Planning PSI
- 36
- Planning bar
- 2.48
245/40R18
36 psi / 2.48 bar
248 kPa · estimates for this size class
245/40R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
Searches for “245/40R18 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 245/40R18. 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 245/40R18 means
Read 245/40R18 as width / aspect R rim. Nothing in the size string is a pressure. Pressure lives on the car, not moulded as 205 or 55.
Wide touring 18-inch. Rim diameter 18 in; section 245 mm. Estimates on this page assume a typical load index for the passenger car class.
Estimated 245/40R18 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 245/40R18.
| 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 245/40R18 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 |
Placard versus sidewall
This website maps size searches such as “245/40R18 psi”. It does not replace the VIN label. If the two disagree, the label wins.
Cars often seen on 245/40R18
These catalogue models are often seen on 245/40R18 or a close OEM neighbour. Open the vehicle chart for axle-specific PSI and bar.
How to set 245/40R18
- Measure before the school run, not after the motorway.
- Write LF / RF / RR / RL. Do not keep 245/40R18 numbers in your head.
- Add air in short bursts toward the placard, using 36 psi only as a map.
- If one 245/40R18 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 245/40R18.
| 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 245/40R18 |
| 38 °C (heatwave tarmac) | 39 psi | 2.69 bar | 269 kPa | Do not bleed a hot 245/40R18 |
If the door sticker and this 245/40R18 page disagree, the sticker wins.
Questions about 245/40R18
Is 245/40R18 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 245/40R18 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 245/40R18 and not share a sticker.
What is 245/40R18 in kPa?
248 kPa is the planning midpoint (100 kPa = 1 bar). 255 kPa is one PSI higher.
Is the sidewall number correct for 245/40R18?
No. Sidewall PSI or kPa is a maximum for the carcass. Operating pressure is the door-pillar placard.
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.
Handbook: placard · bar vs PSI · cold inflation · all sizes