School me guys! I have a restomod project that will be street/highway driven 95% of the time with a 2.5 BL, 1 inch SL, 285/70/17s. I want the best ride quality I can get. What's the advantage of a 4 link coil system over leafs on the street/highway?
I'm looking at the Krawlers Edge Quad Link Coil system, or just keeping the leafs that come the Wild Horses Premium 2.5 Bilstein suspension kit. Apologies if this has already been discussed as I couldn't find an answer. Thanks!
If ride quality is your driving factor, here are some things to consider:
- In general, leaf springs will ride rougher than multi-link suspension due to internal friction in the leaf packs. You just can't tune that out with spring rate or shock tuning.
- HOWEVER triangulated 4-link is NOT the best for ride quality. This type of suspension is better suited to long-travel race applications like desert trucks. The reason is most 4-links use rod-ends or Johnny Joints to keep the links rigid to promote handling. Especially lateral stiffness, giving you crisp cornering feel. That stiffness sacrifices the tire's ability to recede in the wheel well when it encounters a pot hole, bridge seam, rock, etc, leading to increased noise, vibration and harshness (NVH) in the cab.
- Leaf springs have natural recession compliance, since they are a spring AND they usually are equipped with rubber bushings. Rubber is present in any modern suspension to damp out NVH, so it is possible that a leaf spring will deliver better ride quality than a race-oriented 4-link.
- The BEST suspension for a solid axle is going to be a 3-link with torque arm OR a parallel 4-link with trackbar (like a Jeep). A 3-link or parallel 4-link will beat a triangulated 4-link hands-down because it has the ability to divorce lateral and longitudinal compliance, meaning you can make the suspension stiff laterally using small, stiff bushings or cross-axis ball joints AND make it compliant longitudinally using large, soft rubber bushings to reduce NVH. The 3-link with torque arm has a slight edge on the parallel 4-link because it can further divorce the thrust loads from the torque loads. So to take it a step further, you can make the longitudinal links even softer without worrying about excessive axle wrap. The downside is that 3-link/torque arm is the hardest to package.
- Other considerations are spring rate and shock tuning. Spring rate is a little trickier than it appears at first because it has many down stream effects. OE dynamics engineers examine the natural frequencies of the front and rear, which are a combination of spring rate and sprung mass. The rear will always be a higher frequency than the front in order to reduce excessive pitching when a bump is encountered at speed. This means that if your truck has a 50/50 weight bias, your rear spring rate should be higher than your front. If the rear is lighter than the front, you may be closer to the same spring rate f/r, but the rear system frequency will be higher.
- Soft springs are generally better for passenger comfort, but too soft and it will feel like a boat on the water. (again bad). Interestingly, American engineers still tune slightly softer than their European counterparts. You can ride in some American cars and tell they were tuned by a European.
- SHOCKS: A person could spend a lifetime learning shock tuning. The easy answer is buy Bilstein digressively damped shocks that are tuned specifically for a Bronco. The only way to get better shocks is to learn to tune your own and buy rebuildable/ tune-able shocks like Bilstein 7100s or Fox coilovers.
- SWAY BARS: Sway bars are usually required for solid axle applications. Roll rate in a corner is determined by Center of Gravity, Roll Axis height, suspension geometry and spring rates. Solid axle vehicles have naturally low roll stiffness due to the inherent geometry of solid axles. (vs IFS/IRS)
DO NOT try to fix a roll stiffness issue with shocks or springs alone. Spring rate should be driven by straight-line ride performance. Shocks are mostly driven by straight-line performance. Some excessive DYNAMIC body roll can be handled by shocks, but sway bars should be used to tune body roll AFTER everything else is set. (springs/shocks/geometry, etc)
