Martin Motors · Bubble · kPa
231 kPa front, 231 kPa rear — Martin Motors Bubble
- Drivetrain
- front-wheel drive
- Body
- passenger car
- PSI F / R
- 32-35 / 32-35
- Bar F / R
- 2.2-2.4 / 2.2-2.4
kPa
231 / 231
2.31 / 2.31 bar · 32-35 / 32-35 psi
32-35 psi F · 32-35 psi R · 2.2-2.4 / 2.2-2.4 bar · 231/231 kPa
If your gauge only speaks kPa, aim near 231 / 231 for this Bubble, then fine-tune to the placard. A 10 °C overnight drop takes roughly 1 psi (0.07 bar) off a closed Martin Motors tyre.
kPa, bar and PSI
kPa-led conversions. 220 kPa is 2.2 bar and about 32 psi — handy if this Bubble sticker uses SI units.
| kPa | Bar | PSI |
|---|---|---|
| 207 | 2.07 | 30 |
| 221 | 2.21 | 32 |
| 228 | 2.28 | 33 |
| 231 | 2.31 | 33.5 |
| 241 | 2.41 | 35 |
| 248 | 2.48 | 36 |
| 262 | 2.62 | 38 |
| 276 | 2.76 | 40 |
| 303 | 3.03 | 44 |
| 345 | 3.45 | 50 |
| 414 | 4.14 | 60 |
Estimated pressure by tyre size (195/65R15 and others)
195/65R15 is the first planning size here. 215/50R17 is usually the plus-size or LT step. Keep load index at or above original equipment.
| Tyre size | Front PSI | Rear PSI | Front bar | Rear bar | Front kPa | Rear kPa | Note |
|---|---|---|---|---|---|---|---|
| 195/65R15 | 34 | 34 | 2.34 | 2.34 | 234 | 234 | Very common compact |
| 225/40R18 | 36 | 36 | 2.48 | 2.48 | 248 | 248 | Low-profile 18-inch |
| 215/50R17 | 35 | 35 | 2.41 | 2.41 | 241 | 241 | Plus-size 17-inch |
| 225/45R17 | 35 | 35 | 2.41 | 2.41 | 241 | 241 | Sport 17-inch |
| 185/65R15 | 33 | 33 | 2.28 | 2.28 | 228 | 228 | Small / older car |
| 225/50R17 | 35 | 35 | 2.41 | 2.41 | 241 | 241 | Touring 17-inch |
| 205/60R16 | 34 | 34 | 2.34 | 2.34 | 234 | 234 | Taller 16-inch |
| 205/55R16 | 34 | 34 | 2.34 | 2.34 | 234 | 234 | Typical mid-compact OEM |
Martin Motors Bubble placard versus sidewall
The tyre-information placard on a Martin Motors Bubble sits on the driver’s door pillar (sometimes the fuel-filler flap). Catalogue figures here are a general band: 32-35 / 32-35 psi.
Temperature drift
Roughly 1 psi per 5–6 °C. The table uses 34 psi as a 20 °C baseline for this Bubble.
| Ambient | Gauge (front mid) | Bar | kPa | Note |
|---|---|---|---|---|
| −5 °C (hard frost) | 31 psi | 2.14 bar | 214 kPa | Gauge reads low; do not overfill once warm |
| 0 °C | 32 psi | 2.21 bar | 221 kPa | Gauge reads low; do not overfill once warm |
| 8 °C (UK winter morning) | 33 psi | 2.28 bar | 228 kPa | Gauge reads low; do not overfill once warm |
| 20 °C (set cold here) | 34 psi | 2.34 bar | 234 kPa | Baseline |
| 30 °C | 36 psi | 2.48 bar | 248 kPa | Do not bleed a hot tyre |
| 38 °C (heatwave tarmac) | 37 psi | 2.55 bar | 255 kPa | Do not bleed a hot tyre |
How to set the Bubble
- Park the Martin Motors Bubble for at least three hours (cold tyres).
- Use a calibrated gauge, not the only meter on a forecourt hose.
- Set the placard for that axle — about 32-35 psi / 2.2-2.4 bar front and 32-35 psi / 2.2-2.4 bar rear on this catalogue row.
- Recheck all four. A 2 psi miss on a front-wheel drive Bubble is enough to feel a pull.
- Refit valve caps and reset TPMS if the handbook asks for a relearn.
Load notes
Load moves the rear of a passenger car first. If the factory placard already has a “laden” column, use that instead of these sketches.
| Condition | Front (est.) | Rear (est.) |
|---|---|---|
| Driver only | 34 psi / 2.34 bar | 34 psi / 2.34 bar |
| Full occupancy | 35 psi / 2.41 bar | 36 psi / 2.48 bar |
| Motorway + luggage | 36 psi / 2.48 bar | 36 psi / 2.48 bar |
Martin Motors notes
No special Martin Motors exception: the Bubble uses the door-pillar placard. Size estimates on this page only help if you have left the original load index behind.
Spare and inflator kit
A matching full-size spare on the Martin Motors Bubble usually follows the higher axle (often the rear, near 32-35 psi). A space-saver is commonly 60 psi / 4.1 bar — read that tyre’s own sidewall. An inflator kit is not a spare; check the sealant date.
If the Martin Motors sticker and this page disagree, the sticker wins.
Other Martin Motors models
Questions about this Bubble
What is that in bar and kPa for the Bubble?
Mid-points are about 2.31 bar (231 kPa) front and 2.31 bar (231 kPa) rear.
What PSI if I plus-size toward 215/50R17?
Keep load index at or above OEM. Low-profile sizes usually stay at or slightly above the placard. Use 195/65R15, 225/40R18 and 215/50R17 as a planning band.
How often should I check a Bubble?
Monthly, before a long trip, and after a 10 °C weather swing. Include a full-size spare.
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.
What tyre pressure should a Martin Motors Bubble use?
Catalogue reference is 32-35 psi front and 32-35 psi rear (2.2-2.4 / 2.2-2.4 bar), cold. Confirm on the door-pillar placard.
Handbook: placard · bar vs PSI · front vs rear · cold inflation