By Jim Kerr
When it comes to refined suspensions, the new Range Rover from Land Rover has it right. It rides on air. Air suspensions are not new. Several cars were offered with air suspension systems in the 1950s. Unfortunately, materials technology back then still had a long way to go and the rubber air bags used in place of steel springs didn’t last. After returning to find their vehicles sitting flat on the ground, most owners soon replaced their air suspension with conventional springs.
Today, materials are much more advanced. Air suspension is used on most large highway trucks, trailers and buses. Its durability is measured in hundreds of thousands of miles. Several passenger vehicles are using air suspension too. Range Rover calls their system Cross-Link electronic air suspension and it offers the best of on-road and off road ride comfort and handling.
The Cross-Link four-wheel independent suspension is the third generation of air suspension used on Range Rovers. MacPherson struts are used in the front with rubber air bags mounted on the top of the struts. Rear suspension uses control arms to position the wheels and separate shock absorbers and rubber air bags to support the vehicle.
One big advantage of using air bags instead of steel springs is reduced unsprung weight. Unsprung weight is defined as the mass that is not supported by the vehicle’s springs. This would include the wheels, tires, hubs, brakes and on independent suspensions, part of the axle, control arms and shock absorbers. Reducing unsprung weight allows the tires to react faster to road irregularities without affecting the vehicle. Superior handling and ride result.
Another benefit of the electronic air suspension on the Range Rover is the ability to change the vehicle’s ride height. Four different heights are programmed into the electronic air suspension control. Three of these are driver-selectable with a console-mounted switch. For on-road driving, the suspension is set to standard height. The computer uses height sensors at each wheel to adjust the air pressure inside each air bag to keep the vehicle level. If vehicle speed is faster than 100 km/h, the computer automatically lowers the vehicle 20 mm for improved high speed handling.
Getting into a full size SUV can be quite a hike for some passengers so the Range Rover suspension can be lowered at the press of a button by 40 mm. Appropriately, this is called Access ride-height and it is only selectable at speeds below 24 km/h. If vehicle speed increases, the computer raises the suspension back to standard height.
Off-road driving is aided by increased ground clearance. The Range Rover air suspension can raise the front of the vehicle 60 mm and the rear 50 mm above standard height. Selecting off-road ride height also activates the Cross-Link suspension control.
The Cross-Link suspension links both front air bags together and both rear airbags together. One control valve is used at each end of the vehicle to control the airflow through the air lines linking the air bags. When a valve is opened, the springs exchange air, making it easier for the wheels to move up and down to follow the terrain. When one wheel is forced up by the ground, the other wheel is force down by the air transferred to that wheel’s air bag, improving the traction on the unloaded wheel.
The Cross-Link suspension concept is very simple. Two airbags are connected by an air line. Computer control of the suspension allows the Cross-Link operation at low speeds while enabling ride height changes at other speeds. The true test of any suspension is in the driving and the Range Rover passes with flying colours.
On the road, the ride is smooth. Bumps and washboard roads are hardly noticeable. Off-road performance is astounding. Other SUVs and 4x4s beat the occupants up as they bounce from side to side on rough uneven terrain. The Cross-Link air suspension reduces the side to side motion so that even the roughest off road course feels more like a ride down a country lane. The added benefit of transferring weight to the unloaded wheels helps traction so the Range Rover can plough through terrain that stops many other vehicles.
Air suspension isn’t perfect. The weakest link is still the air lines that connect each air bag to the compressor and air reservoir. Break an air line and the vehicle will look like a low rider. Fortunately, the Range Rover’s air lines are well protected, helping it to have one of the best on and off-road suspension combinations on the market.