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What is Semi-Air, Air Assist, Auxiliary Air?

Many terms are used in the world of air suspension, and different companies use different terms. Indeed the US and UK use different terms which can cause confusion. For Motorhomes and Vans the term air assist, auxiliary air suspension or semi-air suspension may be encountered? What does this mean?

It generally relates to larger commercial vehicles such as vans which are often converted to motor caravans or motor homes or used as commercial vans. It also predominantly relates to vehicles with rear leaf springs. In a semi-air system an airbag is used in ADDITION to the original suspension. This gives additional load support for heavy motorhomes which are almost always right on the weight limit. Because of this they tend to ride quite poorly on the road, wallowing banging crashing and grounding on ferrier and petrol stations. Almost all are very close to the bumpstops and most new motorhomes we have seen would not pass an MOT when new for this reason. Semi-air lifts the suspension up recovering the lost motion relating to the sag, stabilising the vehicle due to the additional support and also creating additional clearance at the rear to overcome grounding.

This contrasts with full air suspension which entirely replaces the vehicle spring. This type of conversion tends to be far more expensive, and involved. The leaf or coil spring is totally replaced with an airbag and some links. This gives full control of the vehicle which can be lowered often to extremely low levels which aid loading and can maintain the ride height at any load. This is far more versatile and generally has a far better ride quality. This is the reason it is used for Delicate Load solutions (DLS – We have converted vehicles for museums, for computerised Outside Broadcast OB units and for aviation transport vehicles) and for Wheel chair Access (WAV) vehicles. It is a good solution for most commercial vehicles and will make motorcycle loading far easier for example, but considerably more expensive.


In summary semi-air leaves the original suspension in place and can only lift the vehicle. Full air does not leave the original spring in place, is more versatile and can both lift and lower the vehicle. All air suspension conversions reduce driver fatigue and make the vehicles better to drive. To discuss your requirements in person please email

We do not usually stock full suspension kits on the shelf. They are made specifically for you once you place your order. This can take anywhere from a few days for common items to 90 days for unusual or complicated items or items which have a waiting list. If you require a more accurate indication then this can be provided by email and will be provided once any order is placed in any event.

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