Shock angle and travel distance

1. On some modified bikes where the upper shock mount is moved forward the angle looks to be around 45 degree. That doesn’t appear to make the shocks useful. It looks to me like the shock is working against the swing arm. What is the minimum angle from the swing arm to the shock?

2. What is the travel distance of a typical 11.5" aftermarket shock? i.e. Monza from Mikes/xs650direct. Trying to determine the minimum distance between tire and fender.

peterg said:

On some modified bikes where the upper shock mount is moved forward the angle looks to be around 45 degree. That doesn’t appear to make the shocks useful. It looks to me like the shock is working against the swing arm.

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Since you have three pivots... swingarm and upper and lower shock mounts, it works as it normally would. The reason for doing it is that, the greater the shock angle, the greater the swingarm travel will be for the same shock travel. Put plainly, you can have the travel needed for a scrambler (or closer to it) using the same frame, swingarm and shock travel.

Most shock manufactures should specify the travel. For example, the Progressive Suspension '12 series' 11.5 inch has 61mm travel while the 12 inch has 74mm travel. Racetech recommends 13mm clearance between fender and tire when fully collapsed to allow for frame flex. If you go to race tech suspensions website there is this section on measuring swingarm geometry that might be useful? Obviously no need to fill in the form, but good info nonetheless.

http://racetech.com/page/title/G3S Swingarm Geometry

Thanks guys!

Changing the shock angle can very well change the effective rate of your spring(s). For a given spring rate, the more the swingarm moves, compressing the spring less, will effectively keep the rate from multiplying as quickly. Could help, might not.
If the spring is compressed more or less in a straight line between the mounts, you'll go through your travel quicker, but your spring rate will also multiply quicker.
Reading reviews of some of the Monza shocks (I was interested in the piggybacks), most of them seemed to claim that they were too stiff - the piggybacks, anyway. Changing the angle could mitigate this issue if you don't want to swap springs.
I was considering doing just this with a pair of Works shocks that felt awfully stiff.

peterg raises some interesting questions regarding suspension geometry (and I almost flunked geometry!). "On some modified bikes..." could mean moving the upper shock mount up, down, in, out, etc., but how do you calculate the spring rate and shock length required? If one were to combine a brat kit and a stretched swing arm (giving the illusion of a rigid frame), the angle of the shocks becomes significantly flatter than stock, possibly exceeding 45* as peterg suggests. The concept is not without precedent.
Short of trial and error, how would one go about it?

59Tebo said:

Short of trial and error, how would one go about it?

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Well... you could re-learn the geometry you almost flunked....
Or you could take 3 sticks, tubes.... pieces of cardboard... whatever, and pin two pieces together. Call that the swingarm pivot. The third piece is the shock. Move the shock mounts (upper and lower) to various places and measure shock/swingarm travel with different configurations. Like you said, trial and error... only with throwaway bits. Once you figure out what you want, transfer those dimensions to your frame of choice.