John Davis, managing director of Phoenix Truck and Trailer Equipment,
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says hauliers and manufacturers need to pay more attention to the design of vehicles in order to comply with the C&U regulations...
'The subject of lifting axles and their design is not taken seriously'
Why is it that hauliers and fleet engineers have such short memories when it comes to specifying vehicles, particularly in the light of recent trade press reports of wheel losses and bridge bashing incidents?
Over the past few years we have seen major changes in vehicle design, with lifting axles and air suspension. Many fleet engineers will recall being told drive-axle air suspension would cut costs and ensure a constant fifth-wheel height. As they will also remember, the unladen Fifth-wheel height with steel suspensions could be 57in and the laden height could be 48 inches, which could cause havoc with tandem trailer bogies. When vehicle weights went up to 38 tonnes and triaxle trailer bogies became the norm, a constant fifth-wheel height was required. Overnight vehicle manufacturers could guarantee a constant fifth-wheel height with drive-axle air suspension. But truck manufacturers did not offer lifting mid-axles; these were the province of the dreaded converters.
When the truck manufacturers suddenly discovered lifting mid axles, they did not have the experience with this product which many of the professional re
manufacturers of trucks had. This is going to have dire consequences For many operators of new vehicles with lift-up axles, for a number of reasons.
When you purchase a vehicle with a drive air axle, you assume a constant fifthwheel height is guaranteed. That is not always the case. To lift the twin-steer axle and obtain clearance between tyre and the road surface the air bellows on the drive axle are inflated and physically lift the chassis and Fifth wheel. This means the driver must check his overall height, when the axle is raised or lowered.
Many non-steer lifting mids should be looked at very carefully because when they are installed they often have a design weakness due to the shape of the axle. When they are lifted they strike the chassis and can cause long-term chassis damage if not properly maintained. Once again, manufacturers lift the chassis on the drive axle bellows to give sufficient axle lift. Check by lifting your axle with no trailer connected. The RN, wheel should stay at a constant height with the axle clearing the ground by 3-4in and missing the chassis by a minimum of 2in.
With most recently built vehicles which are Fitted with lifting twin-steer, and some very popular non-steer, the only way the axle can be lifted clear of the ground is to inflate the air bellows on the drive axle and lift the chassis and fifth wheel. If the driver measures the height of his vehicle when the axle is not lifted and he tips his load and then lifts his axle, the vehicle will be higher: in some cases 6-8in higher, depending on the trailer length and kingpin setting. I believe the subject of lifting axles and their design is not taken seriously. Indeed I only know of two manufacturers who do take the matter seriously. Bringing all the above into the context of vehicles being roodtested and written about in the trade press, you will note that articles always state whether a vehicle is fitted with mid-axles, but there will be no comment on its suitability for the purpose. To comment on design you must be aware of what you are looking at, and I feel sure that as professionals within the haulage industry you should be taking a closer look at the lifting axles fitted to your vehicles.
• If you want to sound off about a road transport issue write to features editor Patric Cunnane or fax your views (up to 600 words) to Nicky Clarke on 0181 652 8912.