Shocks - Part 1

Most every vehicle on the race track today has a device called a shock absorber.  The shock on a vehicle controls the speed in which the spring associated with it moves.  The more resistance a shock has, the longer it takes to move it through its range of motion.  Or in other words, a shock controls time.  

For every vehicle - track - spring combination, there is also a proper shock to use.  Shocks are rated similar to springs.  They have a pounds of damping rating.  These ratings help determine what shock should be used.  The shock rating usually can be matched with the amount of coil spring control.  Try to keep the shock damping rate within 10% of the spring rate.  If you are running coilovers, then it's easy to match the shock to the spring.  Just put the shock that's the closest in damping to the spring you are using.  However, if the spring is located in a different place than the shock, as on big spring front clips, then the wheel rate for the spring will have to be determined to calculate the dampening of the shock.  For example, AL = a-arm length, SpL = spring mount to frame pivot length and ShL = shock mount to frame pivot length.  The a-arm length (AL) is 16", the spring mount length (SpL) is 8", the shock mount length (ShL) is 13", and the spring rate (SR) is 1000 lbs/in.  The spring motion ratio (SpMR) is calculated by taking the spring mount length (SpL) and divide it by the a-arm length (AL) then square the answer.  The shock motion ratio (ShMR) is calculated by taking the shock mount length (ShL) and divide it by the a-arm length (AL) then square the answer.

                                      

To determine the proper shock usage, the formula is:

[SpMR ShMR] x SR = Shock rate

SpMR = 8 16 = .5       .5 x .5 = .25 (SpMR)

ShMR = 13 16 = .6602        .8125 x .8125 = .6602 (ShMR)

[.25 (SpMR) .6602 (ShMR)] = .3787 x 1000 (SR) = 378.7 Shock rate.

So in our example, we would need about 380 lb shock damping.  Next tip, we'll go over the shock numbering system.

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