Caterham · 21 · Rear
Rear axle PSI and bar on the Caterham 21
- 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
psi rear
34
2.31 bar · 231 kPa at the rear axle
32-35 psi F · 32-35 psi R · 2.2-2.4 / 2.2-2.4 bar · 231/231 kPa
Loaded 21 rears often need the sticker’s second column, not a copy of the front 32-35 psi figure. Under-inflation cooks the shoulders of a 21; over-inflation wears the centre rib and bangs every cat’s eye.
Caterham 21 placard versus sidewall
The tyre-information placard on a Caterham 21 sits on the driver’s door pillar (sometimes the fuel-filler flap). Catalogue figures here are a general band: 32-35 / 32-35 psi.
Estimated pressure by tyre size (215/55R16 and others)
Planning cold pressures for sizes often seen on a passenger car. This 21 sample opens with 215/55R16, then 225/50R17 and 225/40R18.
| Tyre size | Front PSI | Rear PSI | Front bar | Rear bar | Front kPa | Rear kPa | Note |
|---|---|---|---|---|---|---|---|
| 215/55R16 | — | 35 | — | 2.41 | — | 241 | Slightly wider 16-inch |
| 225/50R17 | — | 35 | — | 2.41 | — | 241 | Touring 17-inch |
| 225/40R18 | — | 36 | — | 2.48 | — | 248 | Low-profile 18-inch |
| 215/50R17 | — | 35 | — | 2.41 | — | 241 | Plus-size 17-inch |
| 205/55R16 | — | 34 | — | 2.34 | — | 234 | Typical mid-compact OEM |
| 205/60R16 | — | 34 | — | 2.34 | — | 234 | Taller 16-inch |
| 185/65R15 | — | 33 | — | 2.28 | — | 228 | Small / older car |
| 245/40R18 | — | 36 | — | 2.48 | — | 248 | Wide touring 18-inch |
Pressure against load
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 | 37 psi / 2.55 bar |
A family passenger car with a boot full of luggage should use the laden rear figure if Ford, VW or Mercedes printed one. Otherwise the modest steps in the load table are only a sketch for this 21.
How to set the 21
- Measure before the school run, not after the M25.
- Write LF / RF / RR / RL. Do not keep 21 numbers in your head.
- Add air in short bursts toward 34 psi (2.31 bar) front and 34 psi rear.
- If one corner is 4 psi down, hunt for a nail before you blame the weather.
- Log date, ambient temperature and the four readings.
PSI, bar and kPa
PSI-led conversions for the Caterham 21 band (32-35 / 32-35).
| PSI | Bar | kPa |
|---|---|---|
| 30 | 2.07 | 207 |
| 32 | 2.21 | 221 |
| 33 | 2.28 | 228 |
| 33.5 | 2.31 | 231 |
| 35 | 2.41 | 241 |
| 36 | 2.48 | 248 |
| 38 | 2.62 | 262 |
| 40 | 2.76 | 276 |
| 44 | 3.03 | 303 |
| 50 | 3.45 | 345 |
| 60 | 4.14 | 414 |
Temperature drift
Roughly 1 psi per 5–6 °C. The table uses 34 psi as a 20 °C baseline for this 21.
| 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 |
Caterham notes
No special Caterham exception: the 21 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 Caterham 21 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 Caterham sticker and this page disagree, the sticker wins.
Other Caterham models
Questions about this 21
What is that in bar and kPa for the 21?
Mid-points are about 2.31 bar (231 kPa) front and 2.31 bar (231 kPa) rear.
When does TPMS warn on a Caterham 21?
Direct TPMS typically flags about 25% below placard — near 25 psi on this row. Fill to the sticker, not to the lamp.
Is the sidewall number correct on a Caterham 21?
No. Sidewall PSI is a maximum. The 21 placard is the operating target, near 32-35/32-35 psi.
How often should I check a 21?
Monthly, before a long trip, and after a 10 °C weather swing. Include a full-size spare.
What tyre pressure should a Caterham 21 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