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Proper Ride Height and Axle Lift Set-up
We have noticed, on our roads, that vehicles fitted with BPW axles and air suspensions are running with very low ride heights. In some instances vehicles fitted with an axle lift can be seen, where the lift axle tyres are raised only a couple of centimetres off the ground. Due to this, tyres can be seen with flat spots because of scuffing on our bumpy roads and also accelerated wear of moving parts in the axle lift device.
Understanding the suspension configuration and ride height.
BPW produces a range of air suspensions to accommodate different ride height requirements. (Please contact BPW for installation instructions on BPW air suspensions). In principle the method of setting the ride heights on all series of BPW air suspensions is the same.
The ride height will also depend on the suspension configuration, where the over slung (see figure 1 and 2 below) will provide high/medium chassis height. The under slung (see figure 3 below) will provide lower chassis height.
Figure 1: Over slung high ride height. Figure 2: Over slung air with medium ride height.
Figure 3: Under slung for low ride height.
Setting your ride height.
The following is a procedure that must be adhered to when setting the ride height:
BPW air suspension axles are manufactured to accommodate a levelling valve. The levelling valve regulates the air bag pressure according to the respective load, thereby holding the vehicle at a constant level.
The levelling valve has to be installed and set correctly as follows:
The levelling valve is normally connected to the centre axle of a tridem, and to the rear axle of a tandem.
Under special circumstances (e.g. axle lift device or extreme vehicle inclinations), the levelling valve can also be linked to the front or rear axle.
Confirming your ride height.
To ensure that all the installations were done correctly it is recommended to confirm your ride height. The measured ride height needs to be confirmed within the allowable limits stated below.
Confirming that your ride heights are within the allowable limits:
Figure 5: Axle lift and required ride height.
The rectifying of the ride height can be done as follows:
More detail on your axle lifts
Multi axle suspensions are frequently equipped with axle lifts to reduce both tyre wear and fuel consumption in both partially laden and unladen state. When it comes to air suspension, this functionality can be realised simply, and controlled or regulated electronically in a suitable manner.
Type of BPW axles lifts
BPW have two types of axle’s lifts available (see figure 6 and 7 below): The centre axle lift (used in the under slung configuration) and double sided axle lifts (used for the over slung configuration). The centre axle lifts uses an air bag to generate a moment on and around a pivot point (centre hanger) to lift the complete axle in the centre. The double sided axle lifts uses single diaphragm boosters mounted to the hangers on each side and use the trailing arm to lift the axle.
Figure 6: Double sided axle lift. Figure 7: Centre Axle lift located in the centre
Located to the hanger brackets. of the chassis with a separate hanger bracket.
Ensuring that ride height is set correct to achieve sufficient ground clearance for tyres.
It is crucial to ensure sufficient tyre to ground clearance when axle lifts are in operation. Insufficient tyre clearance will result in accelerated tyre wear and flat spots on the tyres due to scuffing.
To achieve sufficient ground clearance it is sometimes believed to help, by changing the hole position of the axle lift, but this is simply incorrect. The axle lift can only raise the axle until the bump stop in the airbag is reached. To ensure that the axle lifts are installed correctly please refer to BPW user manual or contact BPW if there are any queries regarding this system.
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