Getting the lowdown
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Platform heights are coming down as new European legislation puts pressure on truck operators to make manual unloading less onerous.
Since the beginning of this year EC Directive 90/269/EC has governed the manual handling of loads in the workplace. Its provisions include the maximum weight which an individual should be expected to lift from different heights at arm's length and close to the body (CM17-23 September 1992).
If only because of variations in physique, the requirements are far less specific than most transport industry legislation, with much use of qualifiers such as "appropriate" and "sufficient". But the spirit of the law is clear. If a driver is injured while attempting to lift a heavy crate down from a vehicle platform, any inquiry will make a subjective judgement on the operator's degree of compliance with the directive.
COMPENSATION
A factor when judging any compensation claims will be vehicle platform heights. In anticipation of operator demand for easier off-loading, particularly in the drinks trade, manufacturers have been concentrating on lowering load platforms. Spine-frame and drop-deck conversions are too costly for many companies, and in any case they leave a section of high-level deck over the rear axle.
Low residual values at the end of five or six years make such drastic chassis surgery even more expensive in real terms, while a used low flat-bed rigid is an attractive buy for a multitude of trades.
At the Institute of Road Transport Engineers' Telford show in May a crop of low-height rigid chassis was launched, and all of them took advantage of low-profile tyres. On 22.51n wheels simply moving from a standard 80 to a 70% aspect ratio tyre lowers the chassis by up to 32mm. Michelin's ultra-low-profile 60-Series tyre can reduce platform height by a useful 65mm.
Chassis, suspension, body mourning and floor structure mods can double the height saving of low-profile tyres by exploiting their reduced axle-to-platform bump clearance.
Retrospective fitting of flatter leaf springs to take up some of that bump clearance is another costly exercise, and anyone trying to shave the final millimetre from his platform height will avoid steel springs because they make the unladen chassis higher due to their vertical deflection under load.
The constant ride-height of air suspension avoids the "deflection factor". The ride height can be further lowered by running the air bags only partly inflated, using the lowprofile tyres' unwanted bump clearance. This is not recommended by the manufacturers, however. Ride quality will surfer, particularly when fully laden, because the natural frequency of the airspring is disturbed and the suspension will jolt as its full-deflection internal bump stops make more frequent contact.
Hendrickson Norde chief engineer Dick Roberts says the most satisfactory solution is to remount each air-spring mounting higher on the side of the chassis; but this is not possible when they are located directly under the chassis sidemembers.
At Telford, Scania exhibited a 17tonne P93MLdownplated to 12 tonnes GVW—with a frame-top height of just 965mm, helped by 70Series tyres and air suspension. It was built for bed manufacturer Silentnight The total travel in the rear air springs is about 250mm (catering for body demount operations) so Scania was able to reduce the ride height by about 25mm lower to maximise the benefit of moving to lower tyres. Thanks to the modest axle loadings ride quality was not affected by "running soft".
An even lower factory option is available from Scania. The P93MV 17-tonne chassis, one of which has been supplied to Moorland Brewery, has a deeperdrop front axle beam and, at the rear, a packer plate on each side between the axle and the quarter-elliptic axle-locating radius arm has been removed. Frametop level above the 275/70 shod rear axle comes down to 920mm.
Leyland Daf is offering a low-height 60 series 17-tormer with 70-series tyres (315 front: 275 rear), decambered (ie flatter) front springs and air suspension at the rear. Quoted rear frame height is 995mm.
Other ergonomically aware companies making multi-drop deliveries are looking to third axle conversions as a means of lifting payloads but not platform levels. At the IRTE show Seddon Atkinson unveiled a special 6x2 derived from its new Iveco-cabbed 17-tonne Strato 210 plated at 21 tonnes. The original frame
55 is retained but it
sits 120mm lower than in standard 4x2 trim, thanks to the replacement of the 10.5-tonne drive axle by a small-wheeled (single drive) 15.6-tonne plated bogie fitted with 19.5in wheels, shod with low-profile 245/70 twin tyres.
Combined with Hendrickson Norde air suspension they bring frame-top ride height down to just 910nun. It could be even lower but at the cost of an aesthetically and practically unacceptable front-to-rear downward slope. On the front axle, 315/70R22.5 tyres are fitted, combining the dimensional benefits of a low profile with a 7.1-tonne axle capacity. Flatter-than-standard leaf springs help lower the front end, so that when unladen the chassis is close to horizontal (front to rear).
HEADLINES
Three years ago at Telford another lowfloored 6x2 with even smaller bogie wheels caught the headlines. It was a 17-tonne Ford Cargo converted by Drinkwater Chassis Engineering, the company that engineered the first Seddon conversion for AG Barr earlier this year. Using 225/75R17.5 tyres, frame-top height over the bogie was down to 780mm.
A reduction in wheel size from 19.5 to 17.5in brings a frame height benefit of about 25mm. Crucially, it also brings the top of the tyres down below the top of the chassis, making body floor height calculations more frame dependent.
The aim is to get the chassis as low as the small bogie tyres will allow, without a slope. The original frame is therefore cut and stepped-down behind the cab, the stepped joint being the subject of a DCE patent. It comes at the cost of either a bigger than usual cab gap or some intrusion into the floorspace. Interest in similar conversions has been revived by the EC's load handling Directive, says DCE's Chris Drinkwater.
Long before the days of low-profile tyres, Bedford and Ford used to compete strongly for small wheeled low-frame six-wheeler sales, with Schweppes' business the biggest prize. Special 6x2s grossing around 16 tonnes were line-built at Dunstable and Langley, to carry as much payload as a four-wheeled 13 or 14-tonner but, thanks to their 16 or 17in wheels, with a frame no higher than the two companies' 8 or 9-tonne GVW models.
Two modern counterparts made their debut at Telford. Volvo's 19-tonne plated 6x2 is derived from an FL6 14-tonner, which has a headstart in chassis height terms with its standard I9.5in wheels and tyres. Its original 5.6-tonne front and 9.2-tonne drive axles are retained. And a single-wheeled tag axle with the samesized 285/70 wheels and tyres is added. Hendrickson Norde air suspension on the converted chassis' bogie plays its part in holding frame height down to 867mm.
Volvo says that if absolute payload capacity is less critical, smaller (265/70 or 245/70) tyres can be fitted, bringing frame height even lower, to 855 and 831mm. The corresponding GVWs would be reduced to 18.56 and 17.52 tonnes, though Volvo says Michelin is intending to uprate the weight capacity of those smaller tyres.
Hendrickson Norde is converting the first FL614s at Northampton: volume production will be undertaken at Volvo's FL6 factory at Ghent in Belgium.
A lighter 6x2 conversion of a standard twoaxled chassis—this time a 7.5-tormer—has been carried out by Chassis Developments for brewer Whitbread. The base chassis is an Iveco Ford New Cargo 80F 15S. Standardprofile 75-series tyres are retained. So too at the front are the original 17.5in wheels, though the basic 215' tyres are replaced by 235s', which raise the plated axle weight from 3.2 to 3.4 tonnes.
At the rear smaller 16in wheels with 205/75R16 tyres—along with Granning air suspension --are adopted on both the drive axle and the new tag axle, enabling the frame to be lowered to 831mm. The 8-tonne rated bogie enables the New Cargo light urban sixwheeler to be plated at 11.4 tonnes GVW Fl by Alan Bunting