255/40R17 · passenger car · kPa
255 kPa for 255/40R17 tyres
- Size
- 255/40R17
- Class
- passenger car
- Planning PSI
- 37
- Planning bar
- 2.55
kPa
255
2.55 bar · 37 psi · 100 kPa = 1 bar
255/40R17 · 37 psi · 2.55 bar · 255 kPa — estimates. Placard wins.
Kilopascals show up on some Asian stickers and ISO sheets. 255 kPa is the planning midpoint for 255/40R17 (2.55 bar / 37 psi). 100 kPa = 1 bar. 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.
kPa, bar and PSI
1 bar ≈ 14.5 psi; 1 psi ≈ 6.89 kPa. Planning midpoint for 255/40R17: 37 psi = 2.55 bar = 255 kPa.
| kPa | Bar | PSI |
|---|---|---|
| 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 |
| 338 | 3.38 | 49 |
Estimated 255/40R17 pressure by load
Load moves the rear first on a passenger car. If the factory placard already has a laden column, use that — not this sketch for 255/40R17.
| Condition | Front (est.) | Rear (est.) |
|---|---|---|
| Driver only / unladen | 37 psi / 2.55 bar / 255 kPa | 37 psi / 2.55 bar / 255 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 |
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.
Placard versus sidewall
This website maps size searches such as “255/40R17 psi”. It does not replace the VIN label. If the two disagree, the label wins.
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 |
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.
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.
Keep 255/40R17 on the printed band for that car; 37 psi is a size sketch, not a second VIN label.
Questions about 255/40R17
What is 255/40R17 in bar?
37 psi is 2.55 bar. Add a tenth of a bar if the placard’s laden column is higher, which is common on vans that wear this size.
What PSI should 255/40R17 tyres be?
A passenger car planning figure is about 37 psi cold (2.55 bar / 255 kPa). Confirm on the vehicle placard — two cars can share 255/40R17 and not share a sticker.
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 255/40R17?
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