ok guy's how short is too short The bags i'm using will have about 7 inches of travel. I ***uming that the shorter the bar, the tighter the turn the more the axle will move forward when the *** is dropped. i'm sure there is a calculation for this somewhere.
If you are going to use a 4-bar, with the bars of equal length and truly parallel to one another, you need only consider the change in wheelbase. If you need the upper bars to be appreciably shorter than the lowers, you will also need to factor in pinion angle variation. 7 inches is a lot of travel. far more than you will need for road use. If you intend to show off by setting it on the ground, you need to plan the top end for road use and save the bottom of the travel for "parking". I like to plan in 3.5 to 4" of total travel. Of that 3.5-4" of travel, I set up 1/3 for droop when the suspension unloads and 2/3 for compression when the suspension loads. You can do a line and string layout on your kitchen table to see how much the wheelbase will change with a given length of bar. The same approach is used in finding pinion changes, but must be done for the shorter bar, also. The drawing below illustrates wheelbase change through suspension travel. Distance between vertical lines is how much wheelbase will change. This drawing shows how much pinion angle will change through suspension travel. The angle between lines A & B is the variation you will see. Note that the smll circles are the end of the upper bar at high and low travel, the larger circles are the lower bar at high and low travel. Line A p***es through the end of both bars at low position, Line B p***es through at high position. Each bar follows it's own arc. The individual length of the bars, space between them, static angle and position fore & aft, all affect the outcome. Grab one or two poster boards and map out your plan. Use pencil. It will change. I do this using cheapo cad programs that let me draw quickly. You can use a string and a pencil to do the same thing. Map EXACTLY what you will build. Adjust your plan until you get acceptable results. Your actual use will determine how much variation in either wheelbase or pinion angle is acceptable. There is no single correct answer. That help?
OK, I kind of understand what's illustrated above, but I kind of don't. I'm finally setting up my rear end with a parallel 4-link and bags. My ride height will be roughly 4" higher than my "parked" height fully dropped. My question is this; will running a 36" parallel 4-link be ok? I guess what I am asking is, is it a good or bad thing to have longer bars? I ordered shorter bars (28") but SD shipped me 36" on accident. I have room to run the longer bars, I just want to know what the pros and cons are to running different length bars. My pinion angle at ride height will be 4 degrees upwards. For driveline to frame clearance it would help me if the rear pinion rotated closer to 0 degrees or less when I dropped the truck down to park. What would help this happen, a longer or shorter parallel set up. Factor in that all four bars will be the same length. Please help, as I need to decide if I have to send these bars back in exchange for the correct shorter bars. Thanks.
Kind of off topic...but you are using an airbag setup up with parallel links...Are you using and sort of lateral control? Pan-hard for example? Or use your upper bars in a "V" setup to help with lateral axle displacement.
Longer bars are better. A properly designed 4 link will not create pinion change. Trying to make your pinion rotate at "parking" height is counter to the purpose. Now you see what goes on when you pose for the cameras. Set it up where it wil be safe and reliable first. It's hard for me to imagine a scenario that you would modify a frame just to make it lay on the ground. I am the wrong guy to ask about that. I'll spend hours and hours designing a good suspension system that works properly in motion. I couldn't give a rat's *** about how it looks sitting at the cruise in.
It's hard for me to imagine a lot of things others do, but if they want to do them that's their thing. Since I'll never be driving it dropped, pinion angle in that position would not matter as much, clearance would. Thanks for the info.
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