Shocks - Part 2

There are many different shock manufacturers that produce shock absorbers for the racing world.  They usually use a two digit numbering system that is consistent throughout the industry for ease of matching the shocks to your car's spring stiffness or wheel rate.  While the actual shock part number may be longer, there are two numbers that usually tell the stroke and rate of the shock.  

The first number to look for is the stroke of the shock.  For the front suspension you need about a 7 inch stroke, so somewhere in the shock part number will be a 7.  For the rear suspension you want a 9 inch stroke so look for a 9 in the part number.

The second number you want to find will tell the stiffness code of the shock.  Normally this is the next number found after the stroke.  

For example in last month's tip we determined that the shock absorber to control the spring would need a 378.7 lb. shock damping rate.  In the chart below, we find that a 7 code (390 lbs. damping) is the closest.  Since this is a front a-arm that means our shock stroke needs to be 7 inches and our damping code needs to be a 7, so our shock number would be a 77.  You can then call your shock supplier and tell him what shock you need and he'll get the correct one for your vehicle.

Sometimes you need a shock with more compression than rebound or more rebound than compression.  These shocks use basically the same numbering system, however the number may have a  /  or a  -  between the damping and rebound numbers.  A 77/5 would be a 7 inch shock with a code of 7 one way and a code of 5 the other.  Check with your shock manufacturer to make sure which number they use for compression and which number for rebound.

The chart below is an example only.  Not all shocks use these exact damping rates but are usually close.

Code Damping
2 135
3 175
4 220
5 265
6 320
7 390
8 475
 

Next time, still more tips about shocks.

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