I am looking at reworking my rear suspension. My question is what is better three or four link rear suspension? I am not doing any extreme rock crawling but, may run down an occasional slew of rock or come across a logging/USFS trail that is in ill repair. I want something that has decent highway manners . I have looked at Duffs four link which looks really nice but sounds like it might not be good for the highway. I have been looking at Ruff Stuffs three link kit. Lastly, I see guys posting drawings of how they are setting up their rear suspensions. I am by no means geometrically inclined. Is there a rules of thumb in setting up a link type suspension? Thank you in advance for your help. I apologize for my "generic" question I really don't know enough about this stuff to ask an educated question.
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Tough decisions. Without understanding everything, it is easy to mess up. The online calculators help, but honestly a traditional 4-link is not good for ride quality AND handling. You can have one, but not the other. I'm sure someone will be along to argue that point, but have you ever see a modern OE vehicle suspension running a triangulated 4-link?
Your two best options for a linked suspension are a 4-link w/ trackbar. (like a Jeep TJ or JK) OR a 3-link using radius arms and trackbar or torque arm and track bar. The key ingredient is the trackbar. It allows you to divorce lateral and longitudinal forces in your links, which then allows you to optimize bushings rates for each. (In the case of the torque arm, you can customize torque reaction rates as well)
Let me explain quick. With a track bar, one link reacts all lateral loads (cornering). The other links, running length-wise with the truck, react the thrust loads from acceleration and braking. They also transfer shock and vibrations when the wheel encounters pot holes, bridge seams, rocks and ruts. It would stand to reason that if you want a comfortable ride, you want softer bushing in your longitudinal links. But you also want responsive handling, which you can get by putting stiffer joints or bushings in your track bar.
With a traditional triangulated 4-link, the links responsible for locating the axle fore/aft are the same ones that located laterally. SO if you put soft bushing in for ride quality, you will lose handling response. If you use rod ends for crisp handling, they will transfer lots of NVH (noise, vibration, harshness)
RULES OF THUMB:
How much energy and brain power do you want to expel? I could dive really deep into this, but it would require backing up and taking a look at the vehicle as a whole. Lets just start by saying that even though a company has a good reputation or sells lots of product, that they know what they are doing. There are many brands of lifts, not limited to Broncos by any means, that are utterly laughed at by true dynamics engineers and in some cases produce dangerous handling characteristics.
But enough doom and gloom.;D
Rules: (and these are very general)
1) Aim to have a higher roll center in the rear than the front.
2) the rear should have a higher ride frequency than the front. How much higher depends on speed/wheelbase etc.
3) the rear should have a lower roll-rate than the front.
4) Aim for reasonable anti-squat, but don't obsess about it. There is no magic number and what you end up with is usually a by-product of the above. Higher #s produce better launches, if you like drag racing, lower allows the axle to better follow the terrain.
