In the UK, air bag suspension has become the preferred option for commercial trailers, overtaking traditional leaf spring systems. This shift reflects the advantages air suspension provides in ride quality, load protection and compliance with weight regulations.
Modern and Road-Friendly
Compared with leaf spring systems, air suspension provides a smoother and more controlled ride. The reduced vibration helps protect both the trailer structure and the load. UK regulations also recognise its road-friendly characteristics, which can support higher Gross Vehicle Weights (GVW) in certain combinations.
Adjustable Ride Height
A key feature of air suspension is the ability to adjust ride height to suit operational needs:
- Running height: The normal operational height of the chassis during transit.
- Raising function: Used mainly for tyre replacement, creating additional clearance between the wheel and mudguard to allow removal and refitting.
- Dump function: The engineered 80 mm compression travel below running height. This is designed to allow safe suspension movement during bump events and chassis roll, ensuring the air bags can compress without overloading structural components. Many systems also allow a manual full “dump” to completely exhaust the air and lower the chassis when required, but this is separate from the intended dynamic compression travel.
Total Suspension Travel Explained
Standard air suspension typically provides around 100 mm of lift above running height and approximately 80 mm of dynamic compression (dump). Combined, this offers about 180 mm of total vertical travel. This range provides enough movement for bump absorption, axle articulation and roll control during normal road operation.
High-Lift and Mega High-Lift Suspension
Some applications require significantly more lift — particularly double-deck operations, dock-levelling scenarios and trailers needing greater clearance during manoeuvring. Two enhanced options are commonly specified:
- High-lift suspension: Provides a raise of approximately 180 mm. Including the 80 mm compression travel, this gives around 260 mm of total travel.
- Mega high-lift suspension: Provides a raise of around 230 mm. When combined with the 80 mm compression travel, total suspension movement can reach approximately 310 mm.
These configurations allow the chassis to be elevated well beyond standard limits, offering improved dock compatibility and greater operational clearance where required. Exact travel can vary depending on suspension manufacturer and axle specification.
High-Lift Options for Double-Deck Trailers
Double-deck trailers often require the rear deck to reach conventional loading dock heights (commonly around 1.2 m). High-lift or mega high-lift suspension allows the chassis to rise sufficiently for the upper deck to align with the dock, streamlining loading and unloading.
Automatic Return to Ride Height
Most modern air-suspended trailers include an automatic return-to-ride-height function. When the trailer reaches a set speed, the system restores the suspension to its normal running height, ensuring consistent handling and preventing prolonged operation at raised or lowered positions.
Control Options
Although not legally required, most trailers are supplied with a standard raise/lower valve at the rear. Additional control points can be fitted to suit operational needs:
- Rear-mounted controls: Convenient during coupling, uncoupling or maintenance.
- Internal controls: Installed within the trailer body where internal height adjustments may be required for certain load-handling applications.
Conclusion
Air bag suspension has become the standard for UK trailers due to its ride quality, adjustable geometry, compliance benefits, automatic return-to-ride-height features and flexibility of control options. High-lift and mega high-lift systems extend the capability further, making air suspension suitable for double-deck operations and other specialist applications.
