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ECO HUB & Air Suspension systems

BPW Patented ECO Hub System


Developed in the early 1990s, BPW’s ECO Hub system represented a milestone in economical trailer operation. The complete wheel and hub unit can be removed using a central threaded connection and the DIN ISO tapered roller bearings used can be replaced easily and inexpensively, without having to fit a completely new hub. 


The design of the ECO Hub system follows more than 120 years of experience in the design and manufacture of axles, and the technology used today is a development of axle construction techniques first introduced more than 80 years ago. Generic changes occurred during the 1970s and 80s and these formed the basis for the first low-maintenance BPW ECO Hub-equipped axles.


Specifically designed to cope with the high-duty cycles of modern transport equipment at low maintenance levels, the ECO Hub’s innovative details give a boost in terms of mileage and economy. This achievement has been met by close attention to key areas such as stub axle, bearing selection, sealing arrangements, lubrication development, and bearing adjustment.


Removal of BPW’s patented ECO Hub is simple. Once the hub cap is removed, it allows access to the axle spindle nut and locking device. The axle nut acts as a puller and by unscrewing this nut anti-clockwise until the thread disengages from the axle stub, the complete hub with bearings, seals and spindle nut can be easily removed. The bearing, seals and lubricant remain undisturbed in the hub.


There is no bearing free play required; a bearing pre-load must be set. With the evolution of the ECO Hub system, BPW designers came up trumps. To eliminate the potential of under or over-tightening the hub bearing, the spindle nut has an integrated torque limiter. It is a simple but ingenious design with the nut slipping as soon as the required pre-set is achieved.


BPW Air Suspension Systems


BPW offers two types of air suspension for 9-tonne axles: the conventional sprung steel trailing arm of the Airlight II, Airlight II Round, and Airlight Heavy Duty (AL-HD), and the cast trailing arm of the ECO Air.


Air suspension maintenance very often receives cursory attention within the statutory periodic inspection cycle. However, it is an important sub-assembly and is responsible for connecting the trailer chassis too, and distributing the load onto, the axle.


It must also be remembered that in an air suspension system, the axle beam is an important component of the suspension system. The connection between the axle beam and the trailing arm is key to the performance of the suspension. BPW supplies assembled axles and suspensions to trailer builders. This enables the company to include, within the five-year warranty (three years for vehicles that travel off-road), both U-bolts and spring seats.


Both suspension systems provide the same physical properties, allowing BPW to offer solutions to cater for different types of trailer design and operating conditions. In order to understand the maintenance requirements of an air suspension, it is worth spending a little time understanding the principles of the operations.


Airlight II Round

Airlight II Round The suspension system on a vehicle comprises the tyres, airbags, trailing arms and bushes. It allows relative motion between the trailer chassis and the road whilst still providing support. The suspension system contributes to the vehicle’s road-holding and braking performance to ensure that the trailer’s payload is given the best possible ride quality.




The design of a suspension system is generally a compromise, and this is more so with a trailer where the difference in ground weight varies so much between unladen and fully laden. It is really important to ensure that the tyre is kept in contact with the road at all times, as this is all that gives the vehicle its braking adhesion and lateral stability.


In terms of maintenance, the regime is quite straightforward and involves periodic inspection for wear and damage and checking the security of the fastenings. The air bags contribute very little to roll stability (around 7%); stability is mainly provided by the axle beam and the two trailing arms which combine to form a large U-shaped anti-roll bar.


It is essential, therefore, to ensure that the U-bolts are kept tight. Different types of suspension have different sizes of U-bolts and different requirements for torque settings and methods of checking. BPW service manuals give the procedures for the different suspension systems that it produces. The presence of corrosion around the interface between the spring saddles and the axle beams is a tell-tale sign that the assembly is loose, and attention is required to prevent further secondary damage to the axle beam from movement between it and the spring saddle.


Torque Settings


The U-bolts on the BPW suspension ranges, Airlight II, Airlight II Round and ECO Air, are designed to stretch when tightened to the correct torque and therefore must be replaced along with the nuts and washers if the assembly is dismantled. It is essential to use the correct tightening method settings on U-bolts.


Air Bags


Air bags need to be inspected for damage, leaks, and perishing; this is best done during the statutory periodic inspections. The air bags are made of rubber which naturally starts to age immediately after the manufacturing process is completed. In recent years, legislation has dictated that ageing additives comply with the new directives, and this has shortened the life of air bags. 


Perishing manifests on the roll of the air bag where the rubber rolls under adjacent to the piston, therefore particular care should be given to inspections in this area. Look at the piston for signs of damage from stones, contact with kerbs, or loading bay reversing guides. If the ride height of the suspension is incorrect, or if the trailer has too much slope, then this will cause the air bags to either stretch out or ride on the internal bump stops. Either of these situations will cause damage.


Trailing Arms


Trailing arms need very little attention, save to check for damage. Where single leaf trailing arms are used, BPW always fits a catch plate. This is a strip made from galvanised steel that encompasses the trailing arm and is trapped under the spring plates by the U-bolts. If a trailing arm breaks, the catch plate will hold the axle in place until the vehicle can receive attention in the workshop. This will prevent the tyres and air bags from being damaged due to the axle becoming grossly misaligned.


The catch plate should always be replaced in order to maintain this safety feature. Any detritus that has built-up between the catch plate and the trailing arm should be removed periodically. Dirt build-up in this area will encourage dampness, which will eventually corrode the top of the trailing arm, leaving it vulnerable to breaking. The rubber bush in the eye at the front of the trailing arm gives little trouble. It can be checked by attempting to move the trailer with the brakes on. There should be no more than 2 or 3 mm of movement between the trailing arm and the hanger bracket in the Airlight II suspension.


On the ECO Air suspension, a different method of checking for bush wear is used. This is detailed in the BPW workshop manual. In all cases, the trailing arm pivot bolt should be kept at the correct torque. If the bolt is loosened or removed, then it should be tightened with the trailing arm set up at the normal ride height for the suspension. This will ensure that there is no excessive wind-up of the rubber bush.


Shock Absorbers


Shock absorbers will need to be checked for leaks and security. Again, this is a task for the periodic inspections. It is the shock absorber’s job to ensure that the tyre is kept in contact with the road surface. The shock absorber on a trailer axle is designed to work with a maximum axle load of 9 tonnes. If the trailer is not fully loaded, then the shock absorber is over-damping the axle.


Sometimes, during manufacture, the shock absorber can be overfilled with oil, and this is ejected when the trailer is first used. The oil is ejected as a fine mist and covers the body of the shock absorber. This should be wiped off initially and all should be well, but if misting re-occurs or oil runs down the body of the shock absorber, then it could be faulty and may need to be changed. It is important to keep the shock absorber fixing bolts at the correct torque or it will run loose and the fixings will become damaged.


All air suspensions are designed to run at specific ride heights, and if the trailer is used with the suspension set up at a different height, then damage can occur to air bags, bushes and U-bolts. Some axles are cambered and any deviation in ride height will change the angle of the axle to the horizontal. This will translate the camber into toe-in or toe-out and result in accelerated tyre wear.




29th September 2022


For further press information, contact Rebecca Wesley or Emma Makings-Hone at BPW Limited:

Telephone: 0116 281 6100 | Email: [email protected] | 

[email protected] |