This really is a great thread. Thank you to everyone for being inquisitive and to the point.
A few of you have been discussing body roll and spring rates. There are a couple of additional factors that influence roll.
CG height vs. Roll center: When the vehicle gets taller the CG is higher and this results in more weight transfer when cornering, which with all things being equal would result in more body roll. However the height change also changes the A-arm angle which changes the roll center location. The roll center is the imaginary point about which the chassis pivots in roll. The higher it is the shorter the pendulum to the mass of the vehicle, and the less the weight transfer gets applied to the springs and sway bar.
Steady state roll when you are in a long sweeping turn and holding a constant wheel angle is simply a factor of A-arm geometry, spring rate, and sway bar stiffness. Transient roll “rate” is quite different as you are moving the wheel quickly and inducing roll. This is where the “dual piston” position sensitivity of the ICON has a huge advantage over the internal bypass method. The internal bypass by its nature must flow oil around the piston, on compression there are check valves that give a bit of low speed control but on rebound it is not possible to check it so it is simply a free flow hole. This results in very little low speed control which is in the shock shaft speed realm of body roll. So when you yank the wheel the chassis twitches over to the roll angle very quickly and unpredictably. Luckily the Raptor is a very wide and stable platform, on many vehicles IB would be a sloppy mess. The ICON however has a separate piston that is dedicated to position sensitive tasks. This allows the main piston to be optimized for handling and especially rebound control. Furthermore the rebound side of the piston is digressive. This allows us to obtain more “mid speed” rebound control without too much high speed force that could result in pack up. The features of the main piston are what give it the ability to settle down and regain composure much more quickly.
The sway bar design in the Raptor is a bit different than what is traditionally seen. At low ride heights it acts stiffer and at higher ride heights it acts softer. This can be minor for small changes. Where I noticed the biggest benefit of this is in trail situations where you are trying to articulate the suspension. When a wheel wants to drop into a hole the bar effectively softens and allows the wheel to extend all the way whereas most IFS is horrible at this.
Spring rate: When I first approached the raptor project the stock front was very soft and sluggish to get back to ride height when compressed so I wanted to give it a slight spring rate increase. I knew I could solve the bottom out with the shock so my goal was not to add spring rate to keep from bottoming but to balance the front to rear response a bit. The first rate I tried was 700, I then went to 725 and as the shock tuning progressed I went back down to 675 which is what production ended up being. I made this rate choice by measuring the stock rate and adding just under 10%. The stock rate I measured was 650lb/in. There seems to be some numbers floating around that I am a bit suspect of. All the coil over springs that any of the companies use are of good quality and I am confident that they actually are the rate that they are stated to be. My concern is how the stock spring rates are being determined. The coil over springs are of the “closed and ground” type but the factory coil is a pigtail bottom and open would top. That means that it has to have an upper and lower perch that match the ramp of the coil. This significantly changes the rate if you remove it from its seats, loaded on the tips only, and try and measure it between two flat plates like you would a coil over type. That is why I always measure the assembly to get a true rate. I re measured another stock assembly today in 2 places in its travel and got 640 and 652. Now that being said and the approach for doing what I did explained doesn’t mean that you have to like it. Generally softer springs correlate to a more comfortable ride and we will ultimately support what people want. Also this shock was designed to take a 3-5/8” ID coil which is a standard for many coil companies so you can also swap the coil to whatever you want which traditionally was what coil overs were, a component for the race car builder/tuner to configure as needed.
What you feel? Is it spring rate or shock valving? Let’s take a bump that moves the shock ¼” at 20in/sec shaft speed. With a 600 lb/in spring it would make 150lb force and let’s say at that speed the shock makes 400 lb for a total 550 lb. If this is uncomfortable than it is largely due to the shock. If not let’s take case two: a 2” bump at 20in/sec. the shock still makes 400lb but the spring now makes 1200 lb for a total of 1600lb. If this is uncomfortable it is largely due to the spring. Now consider that the shock makes more force based on speed so that same 2” bump that is sharper makes the shock move faster and now it’s the shocks fault again or is that force necessary to keep from bottoming or maintain stability?
This thread is primarily about the front. A lot of people we talk to think the front is perfect but want advice on how to adjust the rear for their situation. I run on soft most of the time also. Many people we talk to run soft off road and firmer settings on road for a sportier feel. With the effective of the bump piston there is some room for softening either the main piston compression or the CDC valve and I am going to be doing some retuning soon to meet a broader need for our customers.
As far as hose restriction and compression valves go there is a misconception about where heat and harshness comes from. Basically a shock works on restricting flow somewhere in the system and the heat is directly related to the force and stroke of the shock regardless of where it’s generated. Miss sized components such as way too small of a hose can cause harshness but mostly it comes down to tuning and pressure balancing between components. One big benefit of a compression valve is that it also prevents cavitation and allows lower reservoir pressures.
