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W€ i1Tt Sharon Clancy weighs up what's happening in the trailer suspension market—not a high-profile part of truck/trailer advances but one where a few kilograms saved here and there can make all the difference to potential payload and earnings SUSPENSION COMPONENTS Axle developments might have dominated the news on running gears for the past year or so, but manufacturers have not ignored suspensions. Like trailer builders, they have used finite element analysis and computeraided design to trim weight without sacrificing durability A few kilograms here and there may not sound much, but together can make a useful saving on a triaxle trailer. If weight is critical, do check whether components like dampers and gussets are included.
Contrary to what some operators think, the axle alignment adjustment that modern suspensions incorporate is not simply to help trailer builders—it can save money on the road. One effect of a trailer bogie misaligned with the chassis or king-pin is excessive and uneven tyre wear, so making it easy to adjust alignment during build or after an accident can save pounds. the Discos disc-braked offset trailer axle, while its US parent supplies the suspension for SAF's Intraax integrated axle-suspension.
There is more competition in the light truck and van suspension conversion market. Longestablished Drinkwater Chassis Engineering and Granning are being challenged for airsuspension conversion business by GlideRite, which developed its air suspension for its own minibus fleet. Simpler is a mechanical spring suspension conversion from RM Active Suspension.
VAN AND LIGHT TRUCK SUSPENSIONS Unlike larger trucks, most 3.5-tonners and vans have leaf-spring suspension. The air suspension benefits of softer ride, more stability during cornering and floor height adjustment are mostly restricted to vehicles such as ambulances and easy-access minibuses.
Drinkwater Chassis Engineering 01772 456888 Drinkwater says air-suspension is especially beneficial on rear-wheel drive chassis such as the Mercedes Sprinter, which tend to have a nose-down, tail-up attitude. "We can level the suspension. The floor is three inches lower than a leaf-sprung chassis anyway because there is no need to allow for spring deflection. Dumping the air lowers it another four inches or so." For most applications Drinkwater uses its own suspension design. It has a joint venture with Dunlop to develop ECAS (Electronically Controlled Air Suspension).
Glide-Rite 01428 751711 When AMK decided to design an air suspension conversion for its own minibus fleet, simplicity and minimal maintenance were key concerns. On its Glide-Rite suspension the existing leaf spring is replaced with a new front parabolic leaf spring that picks up on the existing front and rear spring hanger brackets. The spring can now articulate, so any suspension movement is taken up by the four air bags, but drive and handling of the vehicle are unaltered because there is no change in the lateral location. Suspension frequency is selected for comfort rather than their loadbearing qualities. An air drier keeps maintenance down (one hour a year, says AMK), and fitting takes eight hours. Price, including fitting, is £2,150.
Granning 01925 810400 Maxidrop is a kneeling version of Granning's two-bag PDL suspension for ambulances and minibuses. Depending on chassis, deck heights can be as low as 230mm. As well as air springs, the conversion includes synthetic bushes to help a smooth ride and lowering action. An automatic air valve, linked directly to the axle, maintains a constant ride height, regardless of load.
ARM Active Suspensions 01342 311177 ARM's Roadmaster is a set of coil springs designed to help leaf springs cope with higher loads, saving wear and tear on shock absorbers and tyres, and to prevent bottoming-out under heavy loads. As soon as the leaf springs start to strain, the stabilisers begin helping. There is no bottoming of the suspension, says ARM, and because the springs are coiled, there is no extra sway or roll on corners. Where the aim is to improve load-bearing capability, Roadmaster, at £300, is a cheaper option than an air-suspension conversion.
TRAILER SUSPENSIONS BPW 0116 2816100 German manufacturer BPW celebrates its 100th anniversary this year. Its axles and suspension are sold as complete packages. The Airlight weighs 441-453kg an axle, including slack adjuster, saving 63kg an axle compared with the previous SL suspension. A new axle hub and shorter, tapered, hanger brackets contribute most of the weight saving. A new hanger bracket is being introduced in May which has a curved instead of straight front edge to save metal and another 5kg per axle.
Most Airlight suspensions have a singleleaf trailing arm. To save weight, the crank on the ALM overslung suspension arm has been reduced by 80mm but without increasing ride height. A double-cranked trailing arm on the BPW rear-steer suspension allows trailer builders to fit the Airlight suspension without having to taper the chassis frame.
Gigant 01858 434813 Gigant abandoned U-bolts with its Protec axle. Instead of welding attachment plates to the axle beams, suspensions are now bolted on using specially shaped attachment plates. Tightening the bolts on the plates to the correct torque flattens the plates out, resulting in a positive clamp on the axle beam. The trailing arm spring has a twin air-bag mount to give trailer builders more flexibility.
Granning 01925 810400 Granning is better known for van and truck suspensions, but its PTS and PTL air suspensions are used on car transporters and stepframe trailers. Ride heights go down to 165mm and capacities are from 10,500 to 12,500kg.
Neway 01299 251663 Unlike its rivals in the European market, American suspension manufacturer Neway Anchorlok International does not make axle hubs, believing the optimum running gear package is best achieved by using different axles to suit the application. It was a pioneer of lightweight air suspension and the use of fabricated trailing arms. It uses three bushes for the pivot and axle connections, rather than Hendrickson's single multi-purpose one, believing it reduces wear and has less potential for axle misalignment.
Neway's latest suspension is the RL94 (RL stands for Real Light), a light version of the overslung AR94/98-series suspensions for 9tonne axles. The beam is made from lighter gauge steel, and the one-piece axle adapter is replaced with a lighter two-piece version. It weighs 144kg per axle, saving 25kg on the AR94. With ROR TE9000 axles, the RL94 is said to weigh 436kg.
IMS 01509 600185 IMS sells German-built SAF axles and suspensions in the UK. The innovative SKIntraax axle/suspension has been in production for 18 months now. A nine-tonne SK axle is married to a Hendrickson air suspension, but instead of a conventional Ubolt, the axle beam and trailing arm are fixed together using a special circular weld. SAF says this method eliminates the cracking often caused by heat build-up during welding. The shock absorber and brake chamber are attached to the trailing arm rather than to brackets welded to the beam, avoiding any welding of the axle beam. A disc-braked version of the Intraax, called Intradisc was launched in March.
Last year SAF redesigned its conventional suspensions, introducing a modular range with ride heights from 200 to 500mm, over or under-slung trailing arms, and spring centres from 980 to 1400mm. One result is a redesigned trailing arm spring, which, together with a new eye bush, it improves stability, says SAF, especially on trailers with high centres of gravity. Maximum CoG for a ninetonne axle load is from 1,850mm to over 3,100mm. Weights for axle/suspension units run from 463kg to 497kg.
Merkur 01978 852141 The name may have changed from ROR Rockwell to Mentor, but the Llay-based manufacturer still claims the lion's share of the UK's trailer suspension market. New from Mentor is FlexLite, a version of the Flexair FL9000 suspension, which saves 30kg an axle, mostly because of a new light trailing arm and shorter hanger brackets. The new arm does restrict it to on-highway operations, though. Ride heights can be varied from 200 to 475mm, although with reduced travel, the Flexite can be as low as 150mm.