Originally Posted by matsonian
Great write-up SweetPee... and thank you all for all the great comments!
Here are a couple images from our website that show visually how the Coils function...
The purpose of Dual Rate, as has been pointed out, provides a longer FREE LENGTH for the most articulation (needed with out 6Pak shocks) without sacrificing the factory ride rate.
Thank you for all the great comments! I am the one that designed these springs and I just wanted to explain the reasons for the design.
1) Our 6 Pak shocks allowed for substantially more wheel articulation
2) Rubicon, Teraflex etc springs were falling out of the buckets with our 6 Pak shocks installed
3) Long Free Length Springs tend to buckle (bend side to side)
4) Long Free Length Springs require a lower spring rate to maintain proper ride height (lower spring rate makes for squishy ride and sagging when jeep is loaded)
5) Progressive Springs do not hold consistant ride heights
6) Progressive Springs experience high stress in a single coil when fully compressed resulting in sagging over time
7) Maintain a short solid height or fully compressed length of the spring
Solution...Dual Rate Springs
Dual rate springs allow us to increase the free length of the spring (The TJ Front Spring is 24 3/4" free length)...with a soft flex spring rate at full droop until it gets to within 1" of the ride height, where it transitions into a firmer spring rate (similar to factory) for the perfect ride.
This added Free Length allows for increased articulation of the suspension and the springs will remain fully seated in the buckets...thus continue to provide force to the wheel.
Just before a Dual Rate Spring is fully compressed most of the coils are still holding the load thus distributing the stress over most of the spring coils. Longer spring life less sagging.
The fully compressed length or solid height of the TJ front springs discussed here are 9.25 inches. Thus you do not sacrafice any up travel even if you use the incredibly short compressed length of the 6 Pak shocks!
Because the upper coils fully compress at 1" below ride height the upper bucket is virtually lowered providing more stability to the spring. This elliminates spring buckling and reduces body sway.
The Dual Rate Spring maintains the firm spring rate from ride height to fully compressed thus reducing sagging from loading that would happen with a longer free length spring with a single (lower) spring rate.
Because our spring rate is a constant at ride height and not variable rate like progressive springs it is much easier to maintain consistant ride heights.
Someone stated that you could use an RC 2.5 Coil and a spacer. This will not work for two reasons.
1) A spacer does not extend or increase in length during droop. The MC Dual Rate Coil does.
2) One could not get to the 24 3/4" free length of the MC Dual Rate Coil without a spacer that would be so long as to drastically affect up travel or soild height of system.
We appreciate all of your feedback. We are committed to developing new technologies to maximize performance of your suspension. We are also commited to proving the performance improvement with facts.
The CTI (Corner Travel Index) score of our TJ with a Rubicon Express 5.5 Long arm kit was 818 before
we installed the MC upgrade kit and the CTI score was 958 after
our upgrade kit. We experienced the same improvement in ride that Sweetpea experienced. In addition, we were able to reduce our rear bumpstop height by 3 1/4".
Please look up Corner Travel Index (CTI) on wikipedia. CTI is a very consistant and accurate method of truly measuring the performance of your suspension.