Spec’ing the Right Suspension for Your Truck

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  Trucks Spec’ing the Right Suspension for Your Truck Jacob Madden Choosing the right suspension Can affeCt not only the performanCe of your vehiCle, but it can also have a resounding impact on your company’s bottom line. Trucks are expensive. as wiTh any piece of expensive equipment, priority should be taken when spec’ing components that have an effect on the performance of the vehicle, the life of the vehicle, the frequency of maintenance, component lifecycle costs, and the comfort and safety
  Trucks are expensive. as wiTh any piece  o expensive equipment, priority should be takenwhen spec’ing components that have an eect on theperormance o the vehicle, the lie o the vehicle, therequency o maintenance, component liecycle costs,and the comort and saety o the operators. Without adoubt, spec’ing the right suspension should be a highpriority or decision makers in the trucking industry. History One o the rst suspensions widely used in the truckingindustry was the walking beam or equalizing beamtandem suspension. Walking beam suspensions are able toequalize the truckload between two drive axles by allowingthe wheels to adjust to uneven terrain by way o a centralpivot point. Some walking beam suspensions containsteel lea springs designed to oer support and stability.Walking beam and steel lea spring suspensions are veryrobust and demonstrate good stability characteristics,with adequate ride quality or most operations.The next generation o suspensions incorporatedrubber into the springing medium. Asapplications became heavier andmore severe toward the middle o the 20th century, rubber blocksuspensions were designedto increase stability overmechanical spring systems.Later developments inrubber technology provideddesigns that oered animprovement in ride overtraditional walking beamand spring systems bydissipating road shock viarubber bolster springs.Some rear suspensionswere designed as a two-stage system to oerexcellent ride quality in the unloaded condition andadditional stability when the truck is loaded and thecenter o gravity increases.Compelled by the drive to improve ride whilemaintaining the same level o stability and handling,suspension manuacturers in more recent years begandeveloping systems that incorporate air spring into thesuspension design to provide even greater ride quality.In such suspensions, the air springs adjust to maintainproper ride height as the load o the vehicle changes,thereby providing a relatively constant ride whetherloaded or unloaded. Air springs were rst used ontrailers and on-highway tractors to protect cargo romexcessive road shock and to provide enhanced comortor the driver. However, recent developments over thepast decade have produced vocational air suspensiondesigns that oer greater protection o the cargo,chassis and body equipment in severe environments.Over the years, research and development, intensetesting and experience have resulted in current designsdeveloped to address past shortcomings. As a result, thecomponents used in air suspensions have become morerobust and lighter weight. More recent air suspensionproducts have also been developed to increase stabilityand handling, and to package within the tire envelopeor component protection. In addition, more advanceddesigns use system geometry that controls torque wind-up and corresponding rame rise, and signicantlyreduces driveline vibration that can cause undue wearand tear on the chassis and body equipment. What to Consider Upront costs should not be the sole actor used todetermine which type o suspension to spec or yourparticular operation. There are our major actors toconsider when spec’ing a suspension:1. Evaluate the application and duty cyclerequirements or the vehicle to make surethe suspension meets your needs. Trucks Spec’ing the Right Suspension for Your Truck Jacob Madden Choosing the right suspension Can affeCt not only theperformanCe of your vehiCle, but  it can also have aresounding impacton your company’sbottom line. 24   WasteAdvantage Magazine June 2010 hdck’ rt         d c  1920. i c  hdck.  s’g t rgt so fo yo T 26   WasteAdvantage Magazine June 2010 2. Consider the perormance o the suspension (stability, handling, ride,etc.) as it relates to your specic industry.3. Liecycle costs, including purchase cost, maintenance and downtime,can have a major “unseen” nancial impact i not considered whilepurchasing the truck.4. Keeping the weight o the truck as light as possible by spec’inglightweight suspensions can translate to numerous benets, especiallyas the weight o other components continues to increase. Application and Duty Cycles  First and oremost, individuals purchasing new trucks need to take a look atthe intended application to make sure that the suspension design is right or theduty cycle o the truck. For instance, i the application is extremely severe (heavyloads, rough terrain, requent turns, etc.), more durable products are required. Thecontinual stop-and-go nature o reuse vehicles can cause pre-mature suspensionwear i the wrong suspension is spec’ed. Furthermore, trucks that have higher centerso gravity require suspensions that provide superior roll stiness characteristics.In addition, the suspension should have a capacity rating that matchesthe intended use or the vehicle. Your choice in capacity should take intoconsideration the gross vehicle weight, the weight o the body and the weighto the intended load, as well as any regional weight laws that might restrictthe amount o load that can be legally carried. The suspension should also berated the same as or higher than the axle capacity rating, so that it is not thelimiting actor or how much load can be carried while in operation. Ensuringthe proper suspension spec is essential to making sure the vehicle operates inthe most ecient manner possible. Performance  The term “perormance” encompasses stability, handling, ride quality, articulationand mobility. Stability is a measure o how well the suspension and chassis resistrolling or swaying, especially when in a turn. Typically, a vehicle’s stability is basedon its rollover threshold, which is determined by measuring the maximum lateralacceleration a vehicle can sustain in a steady turn without tipping over—less roll= more stability. Higher rollover thresholds allow a vehicle to negotiate a steadyturn at higher speeds. For vocational vehicles, higher rollover thresholds allow orimproved vehicle perormance on the job site, and during lane changes and turns.The amount o roll stiness ound within a suspension is the best way to directlyaect the stability o the vehicle (more roll stiness = more roll stability).Handling is a measure o how well the suspension and chassis optimize thelateral cornering perormance o the vehicle in reaction to steering inputs.Handling determines how ast you can drive and what kinds o turns that youcan make while maintaining directional control (an engineering term knownas “yaw” stability), and it has strong eect on the amount o movement or swayin the tail end o the truck, which can dramatically aect vehicle perormance.A suspension with good handling characteristics can give the driver greatercontrol in both on- and o-road conditions.Ride quality is a measure o how road shock aects the vehicle and driver asthe vehicle encounters bumps, potholes and other road irregularities. Driver andpassenger health and comort are directly aected by ride. Rubber suspensionscan provide excellent ride quality, otentimes bridging the gap between thestability o a mechanical suspension and the ride quality o an air suspension.Because o their inherent design, air suspensions provide superior ride quality.Air springs provide a constant spring rate, meaning that the ride is consistentno matter what condition the body is in—loaded or unloaded.Articulation reers to the amount o vertical wheel travel experienced whentraveling over uneven terrain. Articulation has a direct eect on the traction o the vehicle’s wheels. Suspensions with greater articulation and designs that allowthe wheels to move independent o each other enable the wheels to maintaincontinual contact with the ground, thus providing better traction and mobility. Lifecycle Costs  Lowering costs is a priority or almost every business, community orindustry across the continent. The trucking industry is no dierent, andsuspension liecycle costs play a big part in keeping costs down over the lieo the truck. Not only is the upront purchase price to be considered, but theregular maintenance required on the suspension and propensity or downtimeshould also be taken into account. Let’s ace it—trucks can be driven hardwith signicant load constraints over undulating and rugged terrain. Choosinga suspension that will live in the environment where it is used will help tokeep service intervals as ar apart as possible, and thus minimize downtimeand reduce the costs that result rom recurrent vehicle repairs. In regardsto maintenance, consider whether there are any lubrication requirements orspecial maintenance requirements, as well as how quickly wear items will needto be replaced. In some applications, an extended warranty plan, i availablethrough the dealer or suspension supplier, might be appropriate in order to easethe burden o repair costs in the event o unexpected ailure.  a c     d, hdck’haulmaaX w dcd  2002   w-   c  d q w dd .hdck’ primaaX eX  w dcd  2008     dd  d c c c,c  .    WasteAdvantage Magazine June 2010 27 Not only should the suspension itsel last, but thedesign o the suspension should also protect the chassis andbody equipment rom excessive vibration, road shock andpremature wear. Air suspensions provide greater equipmentprotection over traditional mechanical suspensions due tothe air bags’ ability to cushion the equipment and passengerload. Some air suspensions have a unique geometry designedto optimize torque reactivity, signicantly reducing drivelinevibration that causes wear on components.When choosing a company rom whom to buy your nextsuspension, take into consideration the company’s customerservice track record. Examine the design o the suspensionand determine whether or not it will be easy to maintain.For times when maintenance is necessary, check to see i parts are readily available. The goal is to reduce the amounto downtime in which this expensive piece o equipment isunavailable or use. Weight  More than ever, feets are aced with the challenge toreduce weight while EPA engine regulations, as well asanti-idling laws, continue to add weight to the vehicle.While the obvious benets o lightweight suspensionsystems include the opportunity to consolidate routes, aswell as oset engine, emission and idle reduction systemweight increases, numerous articles have been writtenregarding additional weight savings benets. Accordingto industry studies, reducing truck weight can improveuel economy, decrease wear and tear on vehicles, reducehorsepower needed to overcome mechanical resistance o the drivetrain and tires while driving, lower liecycle costsand improve carrying eciencies, especially during drivershortages. In addition, lightweight suspensions can providegreater reedom or the end-user to spec more sophisticatedequipment by osetting the weight o the additionalcomponents. Spec’ing products that can save weight,whether suspension products or other truck components,can help the end user to realize these numerous benets. Impacting the Bottom Line As with any component, your company’s needsshould be evaluated beore spec’ing suspension products.Choosing the right suspension can aect not onlythe perormance o your vehicle, but it can also have aresounding impact on your company’s bottom line. | WA  Jacob Madden   is the Segment Manager for vocational truck suspensions at Hendrickson, l  o cated in Woodridge, IL.Hendrickson is a premier, global manufacturer and supplier of truck and tractor suspensions and heavy-duty springs; trailer  suspensions, controls and nonintegrated axles; truck and trailer lift axles; and bumpers and trim components to the commercial transportation industry. For more information, call (630) 910- 2800.
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