I\'m Confused! What shock lenght do I need!
I did a search to try and find the correct way of determining shock lenght and got some really old and confusing post-they all seem to contradict each other. I also found this article on a web site:
Size really does matter here. It is very important that you use a shock that is the right length and has enough travel in both compression and rebound to dampen the axle it is connected to. In the easiest of all situations, the shock is mounted straight up and down. The measurement is fairly easy. Measure the distance from the suspension bump stop to surface that it makes contact with, and add a ½" for compression of the bump stop. This measurement is your compression travel. Now measure from your upper shock mounting point, to the lower mounting point. For explanation purposes, lets say that the distance from the bump stop to the contact surface is 5.5" and we add a ½" we now have 6". Lets also say that the distance from the top mounting point of the shock to the lower mounting point is 14". Given these two measurements it is easy to see that you have a difference of 8". This 8" measurement is the length of the shock body you would need to control travel, measured from the mounting eye to the top of the shock body, and not limit suspension travel. In this situation you would actually have approximately 8" of rebound or droop travel in the shock and 6" of compression travel.
Measuring Shocks at an Angle
This is when things get tricky, essentially what you need to establish first is the angle you are going to mount the shock. This angle then needs to be compared to the angle of the suspension when it cycles. Again for explanation purposes we will say that the suspension cycles nearly vertically. Now we will say that due to space limitations you need to mount the shock at a 30 degree angle leaning forward of the axle. First lets say that the suspension travels 6" vertically until it contacts and compresses the bump stop as stated in the first example. Next you will need to measure your two mounting points, for explanation purposes lets say this measurement is 12". Your difference is now 6". Now is where things get a bit tricky. The easiest way to determine the length of shock you need is to cycle the suspension from its loaded resting point to the point were it compresses the bump stop. With the suspension compressed again measure the distance from the upper and lower shock mounting points. Again from explanation purposes only lets say that the total distance between these two points is now 9". You can now see that as the suspension cycles through its 6" of compression travel you are only using 3 inches of shock travel, 12" original measurement minus the 9" you now measured. This means that a shock with a measurement from the lower shock eye to the top of the shock body of 9" would not limit suspension compression or rebound for this application.
IS this the correct way to do it?