Foden's air on a tag spring
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• Foden's firm line on the advantages of using 6x4 tractive units has taken a rare turn with the introduction of a 6x2 model with lifting tag axle. There is also the option of full air suspension on its 6x4 artics and a 30-tonne version for heavy haulage of its FF20 tandem axle rubber suspension.
Although Foden still recommends a 6x4 configuration to handle the high torque outputs from engines of 224kW and above, it has produced a 6x2 version using the Neway AR75 air suspended tag axle, which is supplied in kit form by Rubery Owen-Rockwell from its Llay, Wrexham plant.
The trailing axle has a design rating of 9,400kg although for its single wheel application this is limited to 6,000kg alongside the drive axle's 10,500kg. Here Foden recommends fitting the sturdier Rockwell S180E final drive in place of the S160E used in double-drive form. Parabolic leaf springs are used on the driven axle while the trailing one has a full air two-bag system with air lift that gives about 200m (7.5in) of travel.
The main lift control switch is situated below the driver's side of the instrument panel and with the door closed is almost beyond reach to discourage imprudent use.
The traction-assist or air dump valve button is conveniently placed beside the driver's seat on the engine cover and is light in operation.
When pressed down it transfers load on to the drive axle by releasing air for about five seconds after which the system reflates. A further application is necessary to continue the operation.
The S106T 6x2 is plated at 22.50 tonnes GVW and on its base outer axle spread of 4.02m, Foden claims an 11.8m kerb-to-kerb turning circle.
Shorter wheelbases will also be available and these will enable most operators to gain optimum axle loadings within the 15.5m overall limit.
In standard form with the Caterpillar 3306 ATAAC (airto-air charge cooled) 224kW engine, a day-cabbed Foden 6x2 is said to have an unladen weight of 6,498kg.
Sleeper-cabbed models with engines of 224kW (300hp) and above will weigh between 6,650 and 7,390kg depending on specification. Dealer prices will start at around £33,000 in bare chassis-cab form. GKN has taken the first production 6x2 and Foden has also adapted the tag-axle design on an eight-wheeler chassis for the London Brick Company.
Foden's full air suspension for 6x4 tractive units is a Peterbilt system that is over 12 years old and is currently fitted to over 50% of its artic model production in North America.
Air Trac is recommended as suitable for use with fragile loads, livestock carriage and on tanker operations. The first production models on Foden 6x4s will be entering Shell's truck fleet by January 1.
The four-bag system uses tapered-section spring leaves for even stress distribution and has a geometry that gives a high degree of roll stiffness. Air bellows have internal buffers for protection in the event of deflation.
Radius rods transmit acceleration and braking forces to the frame instead of relying on the springs, while a tracking rod controls the axle's lateral movement and reduces strain on the U-bolts and hanger assemblies.
Air Trac uses a frame height control valve which varies the air bag pressure between 0.3 and 4.5 bar (five to 65psi) depending on the load conditions.
According to Foden the Air Trac option is only 50kg heavier than its FF 20 rubber suspension and costs an extra £290.
Foden's FF30 suspension for
heavy haulage tractive units and multi-axle rigids uses rectangular section bolster springs instead of round ones with the FF20. These have a -15°C to +70°C operating temperature range, and use exactly the same roll control arrangement.
Foden recommends that it is matched to its 8.0 tonne front suspension for heavy haulage, giving a tractive unit a 40tonnes GVW rating.