Articulation versus roll stiffness

Articulation refers to vertical wheel travel, i.e. how far up and down the suspension allows each wheel to move. The better the articulation, the better the chances of the wheel remaining in contact with the ground, thus maintaining positive traction.

Roll Stiffness is the rigidity of an object —the extent to which it resists rolling or twisting deformation in response to an applied rotational force.

Articulation and roll stiffness really are trade-offs. So, if your customer desires both, being aware of how the products are integrated into the chassis will benefit the suggestions you provide. Articulation is typically controlled by the truck manufacturer engineers, so regardless of the product capability, there will be limitations. These limitations typically constrain actual articulation to a fairly level playing field, regardless of suspension style.

Roll stiffness is a function of the suspension design. Think of it as a scale with stability and ride quality being at opposite ends. A customer who has a high CG body and utilizes the equipment in a stationary application will typically trade ride for stability. On the other hand, a long-haul operator will prefer the ride quality of an air suspension, which goes a long way to reducing driver fatigue. Your goal here is to strike a balance.

Today’s vocational suspensions bridge the gap between each characteristic, providing good stability with a decent ride. Most of these products utilize a beam and bolster (or rubber block) design. There are also air bag suspensions with a parallelogram style rod geometry that are good crossover choices when the application does not include a high CG body.

As with other areas, ask questions. If chassis component packaging is a concern be aware that some suspensions have arms or springs (mostly air bag suspensions) that extend ahead of the forward drive tire. This will create a longer wheelbase, which in over-the-road trucks will increase trailer gap, negatively impacting fuel economy.

And now….

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