255/35R18 · passenger car · Bar
Recommended bar for 255/35R18
- Size
- 255/35R18
- Class
- passenger car
- Planning PSI
- 36
- Planning bar
- 2.48
bar
2.48
36 psi · 248 kPa · not a second factory sticker
255/35R18 · 36 psi · 2.48 bar · 248 kPa — estimates. Placard wins.
A 255/35R18 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. Under-inflation cooks the shoulders of a 255/35R18; over-inflation wears the centre rib and bangs every cat’s eye.
Bar, PSI and kPa
Convert around the 255/35R18 band. 2.48 bar is about 36 psi — not 23, not 33 unless the maths says so.
| 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 255/35R18 pressure by load
These 255/35R18 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 | 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 |
Placard versus sidewall
The sidewall of a 255/35R18 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 255/35R18 means
Read 255/35R18 as width / aspect R rim. Nothing in the size string is a pressure. Pressure lives on the car, not moulded as 205 or 55.
Rear stagger 18-inch. Rim diameter 18 in; section 255 mm. Estimates on this page assume a typical load index for the passenger car class.
Cars often seen on 255/35R18
These catalogue models are often seen on 255/35R18 or a close OEM neighbour. Open the vehicle chart for axle-specific PSI and bar.
How to set 255/35R18
- Measure before the school run, not after the motorway.
- Write LF / RF / RR / RL. Do not keep 255/35R18 numbers in your head.
- Add air in short bursts toward the placard, using 36 psi only as a map.
- If one 255/35R18 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 255/35R18.
| 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 255/35R18 |
| 38 °C (heatwave tarmac) | 39 psi | 2.69 bar | 269 kPa | Do not bleed a hot 255/35R18 |
A cheap gauge and a monthly habit will do more for a set of 255/35R18 than nitrogen upsells.
Questions about 255/35R18
What is 255/35R18 in kPa?
248 kPa is the planning midpoint (100 kPa = 1 bar). 255 kPa is one PSI higher.
When does TPMS warn on 255/35R18?
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 255/35R18?
No. Sidewall PSI or kPa is a maximum for the carcass. Operating pressure is the door-pillar placard.
What is 255/35R18 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 255/35R18 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.
Handbook: placard · bar vs PSI · cold inflation · all sizes