255/55R18 · SUV / crossover · PSI
255/55R18 tyre pressure in PSI
- Size
- 255/55R18
- Class
- SUV / crossover
- Planning PSI
- 36
- Planning bar
- 2.48
psi
36
2.48 bar · 248 kPa · SUV / crossover planning figure
255/55R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
If someone typed “255/55R18 psi”, they want Imperial. Start near 36 psi on an unladen SUV / crossover, then confirm the vehicle placard. Sidewall max is not the target. Under-inflation cooks the shoulders of a 255/55R18; over-inflation wears the centre rib and bangs every cat’s eye.
Estimated 255/55R18 pressure by load
Load moves the rear first on a SUV / crossover. If the factory placard already has a laden column, use that — not this sketch for 255/55R18.
| Condition | Front (est.) | Rear (est.) |
|---|---|---|
| Driver only / unladen | 36 psi / 2.48 bar / 248 kPa | 37 psi / 2.55 bar / 255 kPa |
| Typical occupancy | 36 psi / 2.48 bar / 248 kPa | 38 psi / 2.62 bar / 262 kPa |
| Motorway + luggage (sketch) | 37 psi / 2.55 bar / 255 kPa | 39 psi / 2.69 bar / 269 kPa |
PSI, bar and kPa
Convert around the 255/55R18 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 255/55R18 means
255/55R18 means a 255 millimetre section width, a sidewall that is 55 percent of that width, on a 18-inch rim. The R is radial construction.
Euro SUV 18-inch. Rim diameter 18 in; section 255 mm. Estimates on this page assume a typical load index for the SUV / crossover class.
Placard versus sidewall
This website maps size searches such as “255/55R18 psi”. It does not replace the VIN label. If the two disagree, the label wins.
Cars often seen on 255/55R18
These catalogue models are often seen on 255/55R18 or a close OEM neighbour. Open the vehicle chart for axle-specific PSI and bar.
How to set 255/55R18
- Measure before the school run, not after the motorway.
- Write LF / RF / RR / RL. Do not keep 255/55R18 numbers in your head.
- Add air in short bursts toward the placard, using 36 psi only as a map.
- If one 255/55R18 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 255/55R18.
| 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 255/55R18 |
| 38 °C (heatwave tarmac) | 39 psi | 2.69 bar | 269 kPa | Do not bleed a hot 255/55R18 |
Keep 255/55R18 on the printed band for that car; 36 psi is a size sketch, not a second VIN label.
Questions about 255/55R18
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 255/55R18 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 255/55R18 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 255/55R18?
No. Sidewall PSI or kPa is a maximum for the carcass. Operating pressure is the door-pillar placard.
What PSI should 255/55R18 tyres be?
A SUV / crossover planning figure is about 36 psi cold (2.48 bar / 248 kPa). Confirm on the vehicle placard — two cars can share 255/55R18 and not share a sticker.
Handbook: placard · bar vs PSI · cold inflation · all sizes