Mercedes-Benz · S 420 · Overview
Mercedes-Benz S 420: 2.2-2.4 bar / 32-35 psi
- Drivetrain
- rear-wheel drive
- Body
- passenger car
- PSI F / R
- 32-35 / 32-35
- Bar F / R
- 2.2-2.4 / 2.2-2.4
psi
34 / 34
Catalogue mid-points, front / rear · 2.2-2.4 / 2.2-2.4 bar
32-35 psi F · 32-35 psi R · 2.2-2.4 / 2.2-2.4 bar · 231/231 kPa
This rear-wheel drive passenger car is filed here with a working range of 32-35/32-35 psi. The pillar sticker on your VIN still overrides the website. Under-inflation cooks the shoulders of a S 420; over-inflation wears the centre rib and bangs every cat’s eye.
Spare and inflator kit
A matching full-size spare on the Mercedes-Benz S 420 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.
Estimated pressure by tyre size (225/40R18 and others)
225/40R18 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 |
|---|---|---|---|---|---|---|---|
| 225/40R18 | 36 | 36 | 2.48 | 2.48 | 248 | 248 | Low-profile 18-inch |
| 245/40R18 | 36 | 36 | 2.48 | 2.48 | 248 | 248 | Wide touring 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 |
| 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 |
| 195/65R15 | 34 | 34 | 2.34 | 2.34 | 234 | 234 | Very common compact |
| 205/55R16 | 34 | 34 | 2.34 | 2.34 | 234 | 234 | Typical mid-compact OEM |
Mercedes-Benz notes
Mercedes often lists comfort versus load. Match the table to how the S 420 is actually occupied that day.
Temperature and a cold gauge
Roughly 1 psi per 5–6 °C. The table uses 34 psi as a 20 °C baseline for this S 420.
| 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 |
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 | 38 psi / 2.62 bar |
Mercedes-Benz S 420 placard versus sidewall
The tyre-information placard on a Mercedes-Benz S 420 sits on the driver’s door pillar (sometimes the fuel-filler flap). Catalogue figures here are a general band: 32-35 / 32-35 psi.
PSI, bar and kPa
1 bar ≈ 14.5 psi; 1 psi ≈ 6.89 kPa. Mid-points on the S 420: 34 psi = 2.31 bar = 231 kPa.
| 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 |
How to set the S 420
- Park the Mercedes-Benz S 420 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 rear-wheel drive S 420 is enough to feel a pull.
- Refit valve caps and reset TPMS if the handbook asks for a relearn.
Keep the Mercedes-Benz S 420 on the printed band; use 225/40R18 and 215/50R17 only as a map for non-OEM wheels.
Other Mercedes-Benz models
Questions about this S 420
Front versus rear on the Mercedes-Benz S 420?
This row is 32-35 F / 32-35 R. Even when they match, a laden rear can justify a higher number if the sticker prints one.
When does TPMS warn on a Mercedes-Benz S 420?
Direct TPMS typically flags about 25% below placard — near 25 psi on this row. Fill to the sticker, not to the lamp.
What tyre pressure should a Mercedes-Benz S 420 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.
How often should I check a S 420?
Monthly, before a long trip, and after a 10 °C weather swing. Include a full-size spare.
Is the sidewall number correct on a Mercedes-Benz S 420?
No. Sidewall PSI is a maximum. The S 420 placard is the operating target, near 32-35/32-35 psi.
Handbook: placard · bar vs PSI · front vs rear · cold inflation