UK · EU reference Tyre Pressure

255/55R18 · SUV / crossover · Bar

255/55R18 bar chart (2.48 bar planning figure)

Size
255/55R18
Class
SUV / crossover
Planning PSI
36
Planning bar
2.48

bar

2.48

36 psi · 248 kPa · not a second factory sticker

255/55R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.

European stickers print bar. 255/55R18 often sits near 2.48 bar on a SUV / crossover (36 psi / 248 kPa). 2.48 bar is not “36 divided by ten”. TPMS typically warns near 27 psi (about 25% below a 36 psi target). That is already a soft tyre.

Bar, PSI and kPa

1 bar ≈ 14.5 psi; 1 psi ≈ 6.89 kPa. Planning midpoint for 255/55R18: 36 psi = 2.48 bar = 248 kPa.

BarPSIkPa
2.2132221
2.2833228
2.3434234
2.4135241
2.4836248
2.5537255
2.6238262
2.6939269
2.7640276
2.8341283
2.9042290
2.9643296
3.0344303
3.1045310
3.1746317
3.2447324
3.3148331

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.

ConditionFront (est.)Rear (est.)
Driver only / unladen36 psi / 2.48 bar / 248 kPa38 psi / 2.62 bar / 262 kPa
Typical occupancy36 psi / 2.48 bar / 248 kPa39 psi / 2.69 bar / 269 kPa
Motorway + luggage (sketch)37 psi / 2.55 bar / 255 kPa40 psi / 2.76 bar / 276 kPa

Placard versus sidewall

The sidewall of a 255/55R18 may say 51 psi or 350 kPa. That is a carcass maximum. Operating pressure is the tyre-information placard on the driver’s door pillar.

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.

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.

Land Rover DiscoveryMazda CX-5

How to set 255/55R18

  1. Measure before the school run, not after the motorway.
  2. Write LF / RF / RR / RL. Do not keep 255/55R18 numbers in your head.
  3. Add air in short bursts toward the placard, using 36 psi only as a map.
  4. If one 255/55R18 is 4 psi down, hunt for a nail before you blame the weather.
  5. 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.

AmbientGaugeBarkPaNote
−5 °C (hard frost)33 psi2.28 bar228 kPaGauge reads low; do not overfill once warm
0 °C34 psi2.34 bar234 kPaGauge reads low; do not overfill once warm
8 °C (UK winter morning)35 psi2.41 bar241 kPaGauge reads low; do not overfill once warm
20 °C (set cold here)36 psi2.48 bar248 kPaBaseline for this size sketch
30 °C38 psi2.62 bar262 kPaDo not bleed a hot 255/55R18
38 °C (heatwave tarmac)39 psi2.69 bar269 kPaDo not bleed a hot 255/55R18

If the door sticker and this 255/55R18 page disagree, the sticker wins.

Questions about 255/55R18

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.

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 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.

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 kPa?

248 kPa is the planning midpoint (100 kPa = 1 bar). 255 kPa is one PSI higher.

Handbook: placard · bar vs PSI · cold inflation · all sizes