Drive-on work where the wheels should stay loaded - wheel alignment above all, plus general inspection, exhaust and underbody work, and storage.

The vehicle sits on its own suspension throughout, which is the condition alignment must be measured in.

It is quick and requires little skill: drive on, chock, raise, and there are no lifting points to identify.

It suits inspection work, underbody checks, exhaust and fuel system work and general servicing.

It is also the standard choice where vehicles need to be stored one above another, which for a fleet short of yard space can be the deciding factor.

What it does not suit, without a rolling jack, is any work needing the wheels off the ground.

Because the wheels stand on the runways - a rolling jack lifts the vehicle clear so suspension, brake and wheel work becomes possible.

A rolling jack bridges the two runways and can be positioned along their length.

It lifts the vehicle by its chassis or axles, raising the wheels off the runway while the vehicle stays on the lift.

That converts a four-post into a wheels-free lift for as long as needed.

Air-over-hydraulic and hydraulic versions exist, and the jack's own capacity must suit the vehicles - it is rated separately from the lift.

For a workshop buying one four-post for mixed work, the jack is part of the specification rather than an optional extra.

Many are free-standing because the load goes straight down through four posts - but the slab must still carry concentrated point loads and the manufacturer's requirement governs.

A two-post lift tries to topple its columns, so it must be anchored; a four-post lift's load path is essentially vertical.

That allows free-standing installation and, on portable versions, castors for repositioning.

The slab still has to support four concentrated point loads without cracking or settling.

Levelling is important: the lift must sit level for the runways to be level and for the locks to engage evenly.

Some manufacturers still require anchoring in certain configurations or where the lift is used for storage, so the instructions govern rather than the general principle.

The equalising cables or chains above all, plus the pulleys, the locks and the hydraulic components.

Cables or chains keep the four corners rising together and carry the load, which makes their condition central to safety.

Inspect cables for broken strands, corrosion, flattening and correct tension along the whole length, particularly where they pass over pulleys.

Pulleys and sheaves wear and their bearings seize, which damages the cable running over them.

Cable tension needs periodic adjustment so the runways stay level and the locks engage together.

Manufacturers usually specify a cable replacement interval regardless of apparent condition, and it should be followed rather than judged by eye.

It is, and that is a common reason for buying one - but the storage duty has its own requirements.

With the runways raised, one vehicle parks above another, roughly doubling the use of a footprint.

The lift must be rated for continuous static load rather than intermittent lifting, and it must rest on its mechanical locks rather than hydraulics.

Ceiling height has to accommodate both vehicles plus the lift structure.

Check whether the manufacturer requires anchoring for storage use even where free-standing installation is otherwise permitted.

Drip trays between the runways are worth having, since a vehicle stored above another will eventually drip on it.