Extra wheels boost braking
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• by Kevin Swallow A drop-down-axle braking system is claimed to reduce HGV stopping distances by 20%.
Southfields bodybuilders' subsidiary Southfields Ancillary Vehicle Equipment (SAVE) has developed the braking unit, which drops to the road from the vehicle's chassis during emergency braking. In tests at 55mph with trucks loaded to 44 tonnes the system improved braking by 9m (see box).
The system, designed by independent engineer Peter Chown, consists of a horizontal swing-down frame with six 355mmdiameter wheels fitted with disc brakes on four-in-line stub axles. A sensor triggers the braking when the system has been in contact with the road for 0.4sec.
When the driver takes his foot off the brake the frame is automatically lifted back up underneath the body. In tests the system is at the back of the trailer to reduce the possibility of jack-knifing. SAVE director Simon Burton says the idea is simple and effective; the test trailers disc brakes are taken from an Austin Montego.
• The system will be launched later in the year and is expected to cast 1350, although no date or price has yet been fixed. Even a production site has yet to be confirmed. Burton says the company does not have the space to produce the braking system in house, and might well market it out to another axle or trailer producer.
It will be offered as an option until legislation is in place to have it fitted as standard. The system is designed to suit retrofitting as well incorporation on line. The prototype weighs less than 250kg, and Southfields expects production models to be lighter. An aerofoil device is available as an optional extra to the drop-down braking system. It is fitted under the trailer, and directs air upwards, creating more downward force during braking.