255/55R18 · SUV / crossover · kPa
255/55R18 kPa inflation table
- Size
- 255/55R18
- Class
- SUV / crossover
- Planning PSI
- 36
- Planning bar
- 2.48
kPa
248
2.48 bar · 36 psi · 100 kPa = 1 bar
255/55R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
If the gauge only speaks kPa, 248 kPa is the sketch for this SUV / crossover size. Fine-tune to the vehicle that actually wears 255/55R18. A 10 °C overnight drop takes roughly 1 psi (0.07 bar) off a closed 255/55R18.
kPa, bar and PSI
1 bar ≈ 14.5 psi; 1 psi ≈ 6.89 kPa. Planning midpoint for 255/55R18: 36 psi = 2.48 bar = 248 kPa.
| kPa | Bar | PSI |
|---|---|---|
| 221 | 2.21 | 32 |
| 228 | 2.28 | 33 |
| 234 | 2.34 | 34 |
| 241 | 2.41 | 35 |
| 248 | 2.48 | 36 |
| 255 | 2.55 | 37 |
| 262 | 2.62 | 38 |
| 269 | 2.69 | 39 |
| 276 | 2.76 | 40 |
| 283 | 2.83 | 41 |
| 290 | 2.90 | 42 |
| 296 | 2.96 | 43 |
| 303 | 3.03 | 44 |
| 310 | 3.10 | 45 |
| 317 | 3.17 | 46 |
| 324 | 3.24 | 47 |
| 331 | 3.31 | 48 |
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 | 36 psi / 2.48 bar / 248 kPa |
| Typical occupancy | 36 psi / 2.48 bar / 248 kPa | 37 psi / 2.55 bar / 255 kPa |
| Motorway + luggage (sketch) | 37 psi / 2.55 bar / 255 kPa | 38 psi / 2.62 bar / 262 kPa |
What 255/55R18 means
A 255/55R18 on a SUV / crossover is a geometry. Two cars can share the size and disagree on PSI because mass and axle split differ.
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
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.
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 |
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.
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.
A cheap gauge and a monthly habit will do more for a set of 255/55R18 than nitrogen upsells.
Questions about 255/55R18
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.
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.
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.
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.
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.
Handbook: placard · bar vs PSI · cold inflation · all sizes