Is the shock location of the left rear that big of deal? In some case yes, it is very important to the overall of the car. Now in some class there are rules to where the shock can be and how far it can be laying down, so search your rules and understand what you can do. We are going to look at the 3 different locations and the effects they have on the left rear tire. First let us define the 3 spots that we are talking about.
· Shock in front of axle.
· Shock on top of axle.
· Shock behind axle.
What we are going to do is by moving the shock and which is best for the car. The 2nd part of that question is up for grabs and is kind of a drivers fell deal more than what is best. So, we will look at what each place will do for the car and how it effects the car. We are not going to get all scientific but will tell you how it effects the car and drive at the tire.
Shock in Front on Birdcage:
In my opinion this is the best place to run the shock (4-bar) because it holds the car up better than any other place on the car will, but at the same time will kill traction. The motion ratio to shaft movement is better in the front, this allows the compression in the shock to work better at holding the car up. Understand this: it will not hold the car up but will help, if you want the car to stay up you will need to use the gas pedal to do so. Also shock in front kill drive in the car, the more gas you add the less traction you have. Look at it kind of like this, if your shock makes 40 to 50 pounds of od force than you lose 40 to 50 pounds of left rear spring in the car. When running in the tacky fast or rubber up race add the biggest, highest gas shock you have.
· PRO: Holds car up well.
· CON: Kills left rear drive.
· PRO: Good in rubber.
· CON: Not that good on a 3-link car.
· FIX: Add base valve to shock. (Find a good shock brand)
Remember when running a shock in front keep the gas as low as you can in slick this will help on traction.
Shock on Top of Axle:
Not as common of a thing to do and will cause some fabrication to be done or reach to find the parts to do it. Mounting the shock on top of toward the front of the tube is an attempt to reduce load on the front of the birdcage to increase drive in the car. This works because it frees up the birdcage and adds drive to the car that it was losing from the rod force in front. Sometimes this may require a shorter shock and a valve change, but a standard left rear shock will work well in this area. Shock on top my favorite thing to do NO, but it will work, and is a good thing to do if you can’t find a good base valve shock the run in front of the axle.
· PRO: Adds drive to the car.
· CON: Hard to mount.
· CON: Shock may need to be cut down.
· PRO: Will hold the car up to some degree.
· PRO: Works good on 3-link may not be legal.
Shock Behind Axle:
Shock behind on birdcage means that it will be on a coil over setup, and this will add tons of drive to the car. (4-bar) This is what we are looking for most of the time so anytime you can add drive it is probably a good day. Remember this, the motion ratio when the shock is behind is really bad and the car falls at a very fast rate without very much shaft movement. If you are needing help in holding the car up this is not the best setup for your car, although it will add drive it will upset entry pretty bad. This ill handling effect that the car gets will most likely slow you down more than speed you up. Shock behind is better in a preloaded setup than it is when the car gets to the top of the spring. Now when running a 3-link shock behind can offer some load to the left rear that makes the car good, when doing this it is good to mount the shock off the 3 link mount and more to the axle. Again check rules.
· PRO: Adds a lot of drive to the left rear.
· CON: Car sets down real fast and hard.
· PRO: Is good on 3-link cars.
· PRO: Less moving parts on left rear.
· CON: Car may turn up the track on entry when of throttle.
These are my ideas of the left rear you may have other ideas on how this works or more details about how it works but in general these are the facts as we see them now.
I run a customized center pull three link on a UMP Dirt Modified. Our three link bird cages have coil overs mounted on top of them so that they have no effect on the third link. We can actually unhook our third link and push it with a single finger. So far so good.