HST Parabolic springs
3 Leaf Rear Spring 715.130 H & 715.130 L (load level B)
At the outer ends of the second leaf poly urethane blocs are fitted to prevent steel to steel contact (the whole "Stage 3" range has this feature). The three leaves are held together with two steel clamps, which are riveted to the helper leaf and secured with a bolt, tube and nut (in a similar way as with the 715.140 & 150, see below) and guides the upper leaves. The rubber buffers at each end of the helper are now fixed with a M8 bolt. For payload details please see the technical data sheet.
A remarkable feature of this springs is the 3rd leaf, which functions as a helper leaf. This helper leaf only comes into action when payload is placed in the rear of the vehicle and/or when cornering at higher speeds so it gives the vehicle more stability and versatility then the 715.120 H/L
Why a helper?
The answer is simple: If we design a 3 leaf rear spring similar to the 4 leaf rear spring (715.150) the ride will be less comfortable when unladen due to the relatively high spring rate. On the other hand, the rate of our 2 leaf rear spring (715.120) not high enough for towing/laden use. Here comes the helper leaf in because it acts very little when the vehicle is unladen since the curve of the main- and second leaf will not allow the helper leaf to cut-in but when load is applied this curve will be flatter and thus allows the helper to "help" carrying the load. In other words: the helper leaf is essential for a comfortable and stable ride when fully laden and/or fitted with roof rack or when towing a trailer but also allows maximum comfort when unladen.
Nothing to worry about:
In normal driving position the helper leaf just touches the second leaf and in off-road conditions the helper leaf will stay close to this second leaf due to it's well designed curvature and carefully located clamps therefore it will stay clear from any obstruction or underground.