225/40R18 · passenger car · Bar
Recommended bar for 225/40R18
- Size
- 225/40R18
- Class
- passenger car
- Planning PSI
- 36
- Planning bar
- 2.48
bar
2.48
36 psi · 248 kPa · not a second factory sticker
225/40R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
A 225/40R18 C-type or LT carcass can live far above a hatchback bar figure. This page’s 2.48 bar sketch is for the passenger car class, not every car that can physically mount the tyre. A 10 °C overnight drop takes roughly 1 psi (0.07 bar) off a closed 225/40R18. 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.
Bar, PSI and kPa
Use the table, then set a cold gauge. 248 kPa is 100 × 2.48 bar on this size.
| Bar | PSI | kPa |
|---|---|---|
| 2.21 | 32 | 221 |
| 2.28 | 33 | 228 |
| 2.34 | 34 | 234 |
| 2.41 | 35 | 241 |
| 2.48 | 36 | 248 |
| 2.55 | 37 | 255 |
| 2.62 | 38 | 262 |
| 2.69 | 39 | 269 |
| 2.76 | 40 | 276 |
| 2.83 | 41 | 283 |
| 2.90 | 42 | 290 |
| 2.96 | 43 | 296 |
| 3.03 | 44 | 303 |
| 3.10 | 45 | 310 |
| 3.17 | 46 | 317 |
| 3.24 | 47 | 324 |
| 3.31 | 48 | 331 |
Estimated 225/40R18 pressure by load
These 225/40R18 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 | 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 |
Placard versus sidewall
This website maps size searches such as “225/40R18 psi”. It does not replace the VIN label. If the two disagree, the label wins.
What 225/40R18 means
A 225/40R18 on a passenger car is a geometry. Two cars can share the size and disagree on PSI because mass and axle split differ.
Low-profile 18-inch. Rim diameter 18 in; section 225 mm. Estimates on this page assume a typical load index for the passenger car class.
Cars often seen on 225/40R18
These catalogue models are often seen on 225/40R18 or a close OEM neighbour. Open the vehicle chart for axle-specific PSI and bar.
How to set 225/40R18
- Park so the 225/40R18 tyres are cold (three hours, or less than about a mile).
- Read the door-pillar placard for that car — not the 225/40R18 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 225/40R18.
| 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 225/40R18 |
| 38 °C (heatwave tarmac) | 39 psi | 2.69 bar | 269 kPa | Do not bleed a hot 225/40R18 |
Keep 225/40R18 on the printed band for that car; 36 psi is a size sketch, not a second VIN label.
Questions about 225/40R18
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 PSI should 225/40R18 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 225/40R18 and not share a sticker.
What is 225/40R18 in kPa?
248 kPa is the planning midpoint (100 kPa = 1 bar). 255 kPa is one PSI higher.
Is 225/40R18 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 is 225/40R18 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.
Handbook: placard · bar vs PSI · cold inflation · all sizes