255/40R17 · passenger car · Bar
Recommended bar for 255/40R17
- Size
- 255/40R17
- Class
- passenger car
- Planning PSI
- 37
- Planning bar
- 2.55
bar
2.55
37 psi · 255 kPa · not a second factory sticker
255/40R17 · 37 psi · 2.55 bar · 255 kPa — estimates. Placard wins.
European stickers print bar. 255/40R17 often sits near 2.55 bar on a passenger car (37 psi / 255 kPa). 2.55 bar is not “37 divided by ten”. TPMS typically warns near 28 psi (about 25% below a 37 psi target). That is already a soft tyre. Low-profile {sz} does not want a “softer” pressure to recover ride. Stay at or slightly above the car’s original placard if load index is kept.
Bar, PSI and kPa
Use the table, then set a cold gauge. 255 kPa is 100 × 2.55 bar on this size.
| Bar | PSI | kPa |
|---|---|---|
| 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 |
| 3.38 | 49 | 338 |
Estimated 255/40R17 pressure by load
These 255/40R17 load steps are ± a few PSI from 37. They are not a licence to ignore a printed second column on a van or estate.
| Condition | Front (est.) | Rear (est.) |
|---|---|---|
| Driver only / unladen | 37 psi / 2.55 bar / 255 kPa | 37 psi / 2.55 bar / 255 kPa |
| Typical occupancy | 38 psi / 2.62 bar / 262 kPa | 39 psi / 2.69 bar / 269 kPa |
| Motorway + luggage (sketch) | 39 psi / 2.69 bar / 269 kPa | 40 psi / 2.76 bar / 276 kPa |
Placard versus sidewall
If a forum says “all 255/40R17 run 37 psi”, ignore it. A Qashqai and a Golf can share a size and not share a sticker.
What 255/40R17 means
A 255/40R17 on a passenger car is a geometry. Two cars can share the size and disagree on PSI because mass and axle split differ.
Low-profile sport or plus-size wheel. Rim diameter 17 in; section 255 mm. Estimates on this page assume a typical load index for the passenger car class.
Cars often seen on 255/40R17
255/40R17 is a valid metric size in this register even if it is not on the curated OEM shortlist. Treat the 37 psi / 2.55 bar figure as a class estimate and confirm on the vehicle that actually wears it.
How to set 255/40R17
- Park so the 255/40R17 tyres are cold (three hours, or less than about a mile).
- Read the door-pillar placard for that car — not the 255/40R17 sidewall maximum.
- If the sticker is missing, 37 psi / 2.55 bar is only a passenger car planning figure for this size.
- Set all four with a calibrated gauge. A 3 psi miss on one corner shows up as a wander.
- Refit valve caps and reset TPMS if the handbook asks for a relearn.
Temperature drift
Roughly 1 psi per 5–6 °C. The table uses 37 psi as a 20 °C baseline for 255/40R17.
| Ambient | Gauge | Bar | kPa | Note |
|---|---|---|---|---|
| −5 °C (hard frost) | 34 psi | 2.34 bar | 234 kPa | Gauge reads low; do not overfill once warm |
| 0 °C | 35 psi | 2.41 bar | 241 kPa | Gauge reads low; do not overfill once warm |
| 8 °C (UK winter morning) | 36 psi | 2.48 bar | 248 kPa | Gauge reads low; do not overfill once warm |
| 20 °C (set cold here) | 37 psi | 2.55 bar | 255 kPa | Baseline for this size sketch |
| 30 °C | 39 psi | 2.69 bar | 269 kPa | Do not bleed a hot 255/40R17 |
| 38 °C (heatwave tarmac) | 40 psi | 2.76 bar | 276 kPa | Do not bleed a hot 255/40R17 |
A cheap gauge and a monthly habit will do more for a set of 255/40R17 than nitrogen upsells.
Questions about 255/40R17
Is the sidewall number correct for 255/40R17?
No. Sidewall PSI or kPa is a maximum for the carcass. Operating pressure is the door-pillar placard.
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.
Can I run 255/40R17 at a lower pressure for comfort?
Not as a habit. A soft 255/40R17 cooks the shoulders and dulls steering. Keep load index and stay on the placard.
When does TPMS warn on 255/40R17?
Direct TPMS typically flags about 25% below target — near 28 psi if you were aiming at 37. Fill to the sticker, not to the lamp.
What is 255/40R17 in kPa?
255 kPa is the planning midpoint (100 kPa = 1 bar). 262 kPa is one PSI higher.
Handbook: placard · bar vs PSI · cold inflation · all sizes