255/55R18 · SUV / crossover · Overview
255/55R18 tyre pressure
- Size
- 255/55R18
- Class
- SUV / crossover
- Planning PSI
- 36
- Planning bar
- 2.48
255/55R18
36 psi / 2.48 bar
248 kPa · estimates for this size class
255/55R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
255/55R18 is a SUV / crossover size (255 mm section, 55 % aspect, 18-inch rim). A planning cold figure around 36 psi / 2.48 bar / 248 kPa is a starting map, not a second factory sticker. TPMS typically warns near 27 psi (about 25% below a 36 psi target). That is already a soft tyre.
What 255/55R18 means
Read 255/55R18 as width / aspect R rim. Nothing in the size string is a pressure. Pressure lives on the car, not moulded as 205 or 55.
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.
Estimated 255/55R18 pressure by load
Plus-sizing to 255/55R18 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
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
If a forum says “all 255/55R18 run 36 psi”, ignore it. A Qashqai and a Golf can share a size and not share a sticker.
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 |
A cheap gauge and a monthly habit will do more for a set of 255/55R18 than nitrogen upsells.
Questions about 255/55R18
What is 255/55R18 in kPa?
248 kPa is the planning midpoint (100 kPa = 1 bar). 255 kPa is one PSI higher.
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.
When does TPMS warn on 255/55R18?
Direct TPMS typically flags about 25% below target — near 27 psi if you were aiming at 36. Fill to the sticker, not to the lamp.
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.
Can I run 255/55R18 at a lower pressure for comfort?
Not as a habit. A soft 255/55R18 cooks the shoulders and dulls steering. Keep load index and stay on the placard.
Handbook: placard · bar vs PSI · cold inflation · all sizes